Colin Ibbotson’s ‘Skins’ pack

[Dale Wambaugh]

Good stuff!

You know, the real core to all of this is that the stuff in the pack has gotten so light that the concept of a pack full of heavy lumps can be tossed out and solutions like this become practical.

I've thought of using one of the Gerber hydration pack reservoirs as the core for an UL pack. MYOG folk don't have the tooling for molding plastic reservoirs like this, but if you could change the proportions, you could have molded slots for the carbon fiber rods to snap or hook into. A foam pad could wrap around it, but wouldn't need any reinforcement as the reservoir would take all the mechanical stress. It would never be as light as Colin's rig and recycled water bottles though.

[Kevin Beeden]

> Re-reading what I wrote above, I am not sure anyone, including myself will understand what I am asking. :)

You're right there, Steve…

Colin's original had simple sewn loops at each end of the shoulder strap. These fed into slots at top and bottom of the pack, with CF rods at top and bottom, thus holding the strap to the pack.

I thought of adding a a bandolier to the lower strap end, to allow coarse adjustment of length.

The ladderlock idea is to replace the stitched ends completely, and form the end loops with the ladderlock. The loop would still be fed into the slot, rather than unthreading the ladderlock.

The advantages are twofold: the ability to adust the length and position of the straps at both ends, and the ability to re-use the straps from another pack.

HTH.

[Colin Ibbotson]

Hello all! I’m Colin Ibbotson the inventor of the “Skins” pack and I’m extremely pleased and flattered that others can see the advantages of my design and are taking it in new directions. The design is a little over a year old and the latest packs are quite different from the one featured on Andy Howell's blog. The biggest change has been to the frame and how it attaches to the foam. The original design was just too fiddly, particularly with cold hands, so now the carbon frame is permanently attached to the foam and just the straps and skin are removed. The concept is well tested with skins having been produced from many different materials including Cuben Fibre and Dyneema. I took a beefed up “Skins” pack on the 800 mile Arizona Trail earlier this year and it performed better than I could have possibly hoped even when carrying 12kg of food/water + 4kg of kit.

Interest has been considerable from both the walking press and the rucksack industry and there was a possibility that it would be made available commercially. I have however refused to compromise on materials or design to lower production costs so that hasn’t happened. I’ve been very quiet in places like this for a couple of reasons but mainly because of one part of the rucksack that I seriously considered taking a patent out on. The parts in question are the removable hipbelt, the link to the pack and the associated internal frame. This design is unique and allows total and free movement of your hips yet still transfers weight directly to the hips. I’ve decided against the patent now, mainly because of the cost, but also I have a new rucksack design in my head that takes the best of the “Skins” pack but makes it more usable for the average walker. What that means is that I can now put more into the public domain and I would be happy to put up some pictures of the latest designs if you want but it will have to wait till the weekend.

Colin.

[Derek Goffin]

I first heard of this project when I shared my breen cuben order (from the BPL thread) with Colin.
I did not think colin's original system had an inner bag just a load strap with everything wrapped up in his sleeping bag or something.
Kevin's mock up makes things clearer, all sort of things are possible.
What struck me was why do you need horizontal CF rods? Colin does, because he has to connect 4 load points from the shoulder straps to 2 load points on his single load carrying strap. As Kevin has drawn 2 load carrying straps the main need for the CF rods disappears. You could use some buckle to attach the 2 load loops to the shoulder straps at the 4 connection points. The horizontal webbing strips will locate the 4 points horizontally. For light loads what do the CF rods do?
Now I who often carry more weight than Colin does, until he goes to deserts, would transfer the load on the top 2 points to a hip belt with vertical CF rods somehow, thats another issue.

Edit
Colin Had not posted when I wrote this so the above is probably out of date. my apologies

[Kevin Beeden]

Right, I think Steve's comment has just about unravelled in my head.

No, I wasn't intending taking the shoulder strap all the way through the bag, and fastening the ends (although that's what I did with the plastic bag thing in the pictures above).

I envisaged the 50mm webbing as merely a load spreader to protect the mat, and to lock the CF rod, and allow it to connect to the shoulder straps, and transfer the load from the suspension strap (shown with 'Z' truncation in SketchUp; one end goes down to the lower strap webbing, and around the bottom of the load, and back up to the other end, where they are connected with a snaplock fastening).

[Kevin Beeden]

Hi Colin,

Thanks very much for joining in the discussion. I'd really love to see how your idea has progressed, and what your new ideas are; can't wait to see the pictures.

I'll just have to hang fire on making one until I see what you've come up with.

I've got a lot of questions, but I'll let you get settled in before I start…

> I’ve decided against the patent now, mainly because of the cost

Been there, read the UK IPO information, looked into the costs, and went 'eeek!'…

[Kevin Beeden]

Derek,

You could be right that the rods aren't needed, and could be replaced by a buckle of some sort. I left one in place, as I'd shown the suspension straps hanging inside the sholder straps, which would tend to twist the 50mm webbing. The CF rod across the entire back would stop this twisting. I suspect it will also spread the load across the entire back, rather than pulling the webbing through the slot, which may happen otherwise.

However, I guess you could drop the suspension strap from immediately under the sholder strap attachment point.

I'd seen the CF rod as a simple way of attaching the straps, but I was a little concerned about it causing a hot spot, and had thought about (and rejected) a curved rod, or splitting the rod into two pieces.

One of the questions I hope to ask Colin is how much of the load he thinks is carried by the various parts of the pack; I suspect that simple friction between mat and contents will provide some support, so the suspension straps won't take all the load.

[Colin Ibbotson]

Kevin. The upper carbon rod is quite important to the design for 2 reasons. Firstly without it, as you rightly say, the straps will overstress the foam and could pull through. Foam strength varies greatly but the lightest weight stuff I use rips quite easily and needs careful handling. The rod spreads the load over a larger area and in-turn this rod sits on a fabric pad to further dissipate the load. Perhaps If the webbing was substantial enough then that might just work but would also be heavier and quite likely less effective than the simple carbon rod.
Secondly the entire pack contents are suspended from this upper rod using an adjustable strap. This is used to keep the fragile skin as load free as possible and therefore increase pack life. The skin is basically only there for cosmetic/waterproofing with a secondary role as keeping the suspended load under control. The suspended load idea isn’t that important with a dyneema skin but with a lightweight cuben skin it should give a much greater service life. I’ve got a cuben skinned pack that I’m doing a long-term test on at the moment but it will be a while before I have any worthwhile results.
Your also correct that the load hanging strap will not take the entire load and that friction between the load and foam frame will transfer some to the pack. I had thought about that and even considered covering the entire foam frame in cuben or silnylon to reduce the friction but the weight increase didn’t seem worth it. I tighten the load strap quite tight and what it does is reduce the jarring stresses on the pack when walking. On rough terrain those stresses will be substantial.

Careful examination of the Arizona Trail pack showed wear in 2 places.

1. Skin upper strap slits – point where the upper straps pass through the skin and attach to the foam frame – skin fabric had torn here showing the skin was carrying some load, this point has been strengthened on all new packs and is unlikely to cause problems again.
2. This will me meaningless without photo’s but the mechanism I use to attach the pack to a hipbelt uses aluminium tent stakes or carbon rods (if you are taller) fitted with aluminium caps. These rods are free to move when walking and I found that they contacted the skin enough to wear it very thin. The aluminium caps have now been modified to eliminate that problem and I’ve also added dyneema wear pads to the pack in that area.

[Derek Goffin]

I can see without a carbon rod that the load is not spread. I was not suggesting no carbon rod but nearly vertical ones instead of horizontal;I like the weight on my hips. With 2 suspension loops I think it would work. I should wait to see Colins pictures of his tent peg suspension.

[Colin Ibbotson]

“…was not suggesting no carbon rod but nearly vertical ones instead of horizontal….”

I now understand your point Derek. Your idea would work but unless the vertical rods are removable then you would be laying directly on them if you use the frame as your sleeping mat. It could certainly be done though.

[Kevin Beeden]

> Firstly without it, as you rightly say, the straps will overstress the foam and could pull through.

Yes; I was going to post a little diagram showing the forces acting on the CF rod, to explain why it will pull through; there's the vertical force of the suspended load, but there's also an angled force of the shoulder strap, since we're hanging the pack off the shoulders, but also pulling it in towards the body, hence trying to pull the strap, CF rod & mat out through the slit.

> Perhaps If the webbing was substantial enough then that might just work but would also be heavier and quite likely less effective than the simple carbon rod.

I agree.

> Secondly the entire pack contents are suspended from this upper rod using an adjustable strap. This is used to keep the fragile skin as load free as possible and therefore increase pack life.

Yes, understood; I'd proposed two straps (gut feel: seems more stable to me), both sewn to the load-spreading 50mm webbing, and secondarily used to create the CF rod retaining loops.

> Your also correct that the load hanging strap will not take the entire load and that friction between the load and foam frame will transfer some to the pack.

I suspect this is what is causing the tears around the skin slits; the entire Skin & foam is being pulled down by the load (even if it's only dynamically as the load moves about on rough terrain). I assume that you have located the slits to take account of the angled path of the shoulder strap into the skin? I cut them perpendicularly to the CF rod in my plastic bag play thing, but realised that's wrong… The SketchUp model shows them perpendicular, too, but that's only for clarity/convenience…

I imagine that, even with the CF rod and load-spreading on the mat, the attachment point is likely to bulge out a bit, and thus stress the skin fabric. I'd envisaged reinforcing around the slit opening, certainly.

Talking of the slits, did you do something similar to my suggestion of not cutting a mat slot all the way to the edge? I couldn't see why this was needed, and it only seemed to weaken the already vulnerable mat. The only benefit seemed to be a reduction in the need for careful vertical alignment of Skin to mat.

I should stress that all my comments and questions are meant very much constructively, I think it's a great idea, that has fired my designer's mind, and I'm very much looking forward to the pictures…

[Kevin Beeden]

> I was not suggesting no carbon rod but nearly vertical ones instead of horizontal;I like the weight on my hips.

Ah, your first paragraph seemed to suggest eliminating the CF rods; that's what I was addressing. Your second paragraph suggesting vertical rods seemed to be a different, interesting issue…

I need to go away and think about how the load is carried within a conventional rucksack, and how the Skins is different…

…okay; that's not so hard: a conventional pack is a big bag, and the load is suspended by the fabric of the entire bag sidewall and base. Straps are attached to the bag, so that the load is transferred to the straps. The fabric bag doesn't stretch much, so the load cannot slump down. Upshot: the fabric bag is in tension vertically and horizontally (circumferentially). Since there are two attachment points at top and bottom, on one side of the bag, it's possible for the bag to slump, and fold somewhat in the middle (and you can see that happening in lightly packed, or poorly-slung packs; e.g. school bags). That's one reason why packs often have reinforcements of some kind in the back.

With a 'pure' Skins pack, the load is suspended from just the upper CF rod. The mat and pack provide some of the slump-revention function that a conventional pack bag provides; we surround the load with a cylinder of mat and the Skin, which provide a fairly rigid support for the load.

So, how do we transfer load to the hipbelt?

Why can't we simply add a hipbelt and associated suspension point? Provided we can support the load, and transfer that load to the hipbelt: the load becomes a column supported from below, rather than hanging from above.

What purpose does back stiffening perform?
Well, without back stiffening, the pack can slump, as we've discussed above. Without a significant force from above, the fabric of the pack isn't held in vertical tension. Of course, we don't remove all the force from the shoulder straps, just reduce it somewhat.

In the case of a 'pure' Skins pack, with a purely suspended load, we must attach the suspended load from this stiffened back. If we use a single suspension point, some sort of A-frame support sounds plausible. It's starting to sound like an old-skool backpack with a bent steel A-frame and a bag hanging off it…

I'm starting to ramble, so I'd probably better stop…

> Your idea would work but unless the vertical rods are removable then you would be laying directly on them if you use the frame as your sleeping mat.

I'd assumed from the pictures of your prototype that the rods were removable. I went one step further (too far…?) and was going to have the entire webbing separate from the mat, even if this would have made re-assembly a bit trickier…

[Kevin Beeden]

d'oh!

I may have confused Steve (and others) by talking about ladderlock buckles to form loops at the ends of the straps. When I actually meant simple buckles (three horizontal bars between side bars). Like this:

[Colin Ibbotson]

“I'd proposed two straps (gut feel: seems more stable to me), both sewn to the load-spreading 50mm webbing, and secondarily used to create the CF rod retaining loops.”

Agreed, but I only think its necessary with a larger pack. Most of my packs are around 30L and double straps would be overkill, with the larger pack I took on the AZ trail then double straps might have been better.

“I imagine that, even with the CF rod and load-spreading on the mat, the attachment point is likely to bulge out a bit, and thus stress the skin fabric. I'd envisaged reinforcing around the slit opening, certainly.”

That’s exactly what happens and all slits are reinforced (only upper on a dyneema skin).

“Talking of the slits, did you do something similar to my suggestion of not cutting a mat slot all the way to the edge? I couldn't see why this was needed, and it only seemed to weaken the already vulnerable mat. The only benefit seemed to be a reduction in the need for careful vertical alignment of Skin to mat.”

Again you are correct. All packs no-longer have slots all the way to the edge. They are one piece with slits cut only for the straps. Carbon rods and quick release buckles (upper) and ladder locks (lower) remain attached to the foam frame. Assembly/disassembly takes seconds.

“Why can't we simply add a hipbelt and associated suspension point? Provided we can support the load, and transfer that load to the hipbelt: the load becomes a column supported from below, rather than hanging from above.”

Basically what you are doing here is transferring the load from the upper carbon rod through the foam frame to whatever you are attaching your hipbelt to. The problem is that the foam frame just compresses or could even collapse if the pack is only half full. What I do is when I want to use a hipbelt I add a removable carbon rod that links the upper and lower rods. This transfers the load from the upper to lower carbon rod and to this lower rod I attach (again removable) 2 external vertical rods (tent stakes) that link the pack to the hipbelt. The pack effectively hangs from these vertical rods and they are free to rise and rotate with your natural walking style. Without pictures this probably doesn’t make much sense but it’s a very direct method of getting the weight to the hips that can add as little as 30g (including hipbelt) while allowing a natural and comfortable walking style.

“I should stress that all my comments and questions are meant very much constructively, I think it's a great idea, that has fired my designer's mind, and I'm very much looking forward to the pictures…”

Not a problem! New ideas are good… Photo's should be up over the weekend.

[Derek Goffin]

Can't wait for the photos.
When ultra light rucksack manufacturers have used carbon fibre arrow shafts as an internal frame it has not been successful because peoples backs are curved. If you had you lower horizontal rod in the small of your back the straight vertical rod you talk about would lie against your back better than if the vertical rod had to go all the way to your hips. Your tent pegs would then be angled struts and would tend to push the bottom of the pack away from your back?
Yet you say the pack "hangs" from the rods as if the lower rod is lower than the hip belt and the tent pegs are in tension? If the lower rod is that low you have the same problem of the straight vertical internal rod not conforming to your back?
My idea was 2 splayed vertical rods starting at the centre of the back of the hip belt and supporting the 2 suspension straps at the top shoulder strap points. I hoped the splay would avoid some of the curved back problem. I take it back you would need a top horizontal rod as the shoulder straps would need to be attached more centrally than the splayed verticals. The one or 2 suspension loops can be placed more freely
The central support on the hip belt would allow your hips to rock naturally. AArn packs and ULA for example fix their hip belt only at the mid point for this reason

[Colin Ibbotson]

“…not been successful because people’s backs are curved…”

This is quite true and a straight carbon rod isn’t idea. There are 3 solutions to this

Use 2 parallel rods either side of the spine as you suggest. Early packs did just that and connected directly to a hipbelt. For my needs this was heavy, increased assembly time (the rods have to pass through the skin at some point) and this method lacked the feel of my rod/peg system.
Use an aluminium rod for the link that can be bent to your back shape. I intend to try this on the heavyweight packs but for the lightweight pack it would be an overkill and a little heavier.
Use a grade of carbon that flexes enough to bend to the shape of the spine but is still stiff enough to transfer the load. This is what I have done. It’s not perfect but acceptable for my needs.

“…you say the pack "hangs" from the rods as if the lower rod is lower than the hip belt and the tent pegs are in tension…”

The pack does indeed hang from the tensioned pegs but is higher than the hipbelt.

[Derek Goffin]

"Curiouser and curiouser" said Alice.
Now I do need a picture. I can wait (just):)

[Kevin Beeden]

> Why can't we simply add a hipbelt and associated suspension point?

What I was trying to do with that discussion was go through a rational thought process of how a conventional back-mounted load is supported, and how a Skins pack differs from this. Unfortunately, it got a bit garbled during editing to attmept to un-ramble, so that paragraphs are out-of-sequence… I've left it extant, rather than editing, and will try to explain my thoughts below.

Imagine we had a completely rigid load-carrying system. We could support it anywhere; at the top, at the bottom, and the only thing we'd need to do would be to maintain stability.

So, if we supported the load entirely at the base, we'd have a column, supported from the base. However, the base of this column is moving about as we walk, so we'd need something to stop the column falling over; shoulder straps to provide a retaining force.

There are examples of such rigid load-carrying packs that have been around for aeons; woven greenstick (or reed, etc.) baskets. Often used for harvesting:

Wine harvesting baskets

So we now have to consider how a fabric rucksack differs from a rigid rucksack.

In the simplest case of a tube of fabric, the fabric rucksack isn't a rigid column; it will flop about if it's only loosely packed. Again, we need to provide some stability to stop this happening. Either we add stiffening elements, or we suspend the load from the top.

In the case of the Skins pack, the load is suspended from the top, using the suspension strap. The Skin must be considered utterly non-rigid, so we cannot support it from the bottom; it will slump and flop about all over the place.

In which case, we need a means to support the upper suspension point, and transfer that load down to a lower support point.

Now we're into the realm of vertical support elements, and how we go about doing that.

[Colin Ibbotson]

[Derek Goffin]

That is very interesting and compared to your skins pack on Andy's site very slick, and still very light.
The pack without hip belt you can just put on like any pack. How do you get the hip belt on? I can imagine you have to put the belt on then put the pack on and insert the tent pegs into their holsters behind you? Even if there is a way to lock the pegs in their holsters I can imagine getting in a tangle.
Can you sensibly get at any internal pack contents during the day. You unclip the lid, then undo the drawcord, then unbuckle the suspension loop. Does eveything have to be packed in carefully to keep it in the suspension loop so that rummaging during the day is dangerous?
It looks as if your skin cannot be totally waterproof because of the webbing inserts. Does your quilt and spare warm clothes have to go in a dry bag? If that is the case (thinking of Scotland) is there any mileage in a cuben dry bag for everything inside the suspension strap and no complete skin. I am thinking just what is needed to hold the foam mat, water bottles and "front" pocket in place.
Are those kite joints that you use to keep your 3mm? internal vertical carbon rod in place? The ones I know of only come as square T joints, nonetheless I would be interested in avoiding my spine by having 2 rods as close together as possible at the bottom and as far apart as the square joints allow at the top. Do you leave the joints on the horizontal rods at night and just pop the vertical rod out?
I somehow expected that the suspension loop would have to have some sort of location on at least the top carbon rod, but in your photo it just looks like an unadorned webbing loop with a tensioner buckle. I imagined the rod would have to be the highest point of the suspension loop to work.

[Colin Ibbotson]

“The pack without hip belt you can just put on like any pack. How do you get the hip belt on? I can imagine you have to put the belt on then put the pack on and insert the tent pegs into their holsters behind you?”

You put the belt on followed by the pack and then insert the pegs. The belt usually stays on all day and only the pack is removed for breaks etc. System works well and takes no longer than putting on a conventional pack. The pegs can pop out when you bend over so this system isn’t ideal for scrambling.

“Can you sensibly get at any internal pack contents during the day. You unclip the lid, then undo the drawcord, then unbuckle the suspension loop. Does eveything have to be packed in carefully to keep it in the suspension loop so that rummaging during the day is dangerous?”

Access is no different from a conventional ultra light pack except you enter from the bottom! Packing is quite easy – you pack as normal but put something large in last to hold everything in place (I use the tarp). So far nothing has every dropped out or even come loose.

“It looks as if your skin cannot be totally waterproof because of the webbing inserts”

The pack is fully waterproof because any water that gets through the slits or seams only goes as far as the closed cell foam frame. Water can only get in at the top of the pack which is why I built the small rain covers shown on the packs. Water has never passed through to the pack contents but I still pack my sleeping bag etc in a waterproof Cuben drysack for additional protection – the same as I would do with any pack (even if described as 100% waterproof – remember I live in Scotland!).

“Are those kite joints that you use to keep your 3mm? internal vertical carbon rod in place?”

Yes

“Do you leave the joints on the horizontal rods at night and just pop the vertical rod out?”

No. The “T” pieces are glued to the vertical rod but they are modified to allow them to clip in and out of the horizontal rods as needed.

“I somehow expected that the suspension loop would have to have some sort of location on at least the top carbon rod, but in your photo it just looks like an unadorned webbing loop with a tensioner buckle”

No location – just passes around the top rod.

[Kevin Beeden]

Colin,

Thanks for the photos – great stuff!

The side views show the pack sitting very high, so clearly not resting on the shoulders, so the load is clearly being taken on the hip belt. Whether through familiarity or otherwise, I think I'd go for a lower-slung pack, but had been concerned about rubbing of the pack base with the tail of the S-curve at the lower back.

I was playing with hip belt design the other day, and arrived at the same high-back, low front that you have. I say 'design', but it was more a case of 'where are my hips, and how does a belt actually fit around them?'.

Lots to take in, so I shall peruse them at leisure, and probably come back with some more questions…

But here's one; I'm still not sure of the logic of the bottom-fill. I'm not sure what benefit it gives over a conventional top-fill (other than draining, which could be done with a simple drain hole). I'd be grateful if you could explain the philosophy.

[jeans and cotton t-shirt…? you'll get drummed out of the SUL Brownies for that… ;-) ]

[Kevin Beeden]

I was wondering why so many of the wine-harvesting baskets on the page I linked to were conical, as this seemed to be an inefficient use of potential load-carrying.

Then I considered what might happen if you piled a lot of grapes on top of each other in a cylinder; they might start to press themselves…

I suspect the cone acts to limit the load exerted on the lower grapes, because the sloping walls provide some upward force. You can demonstrate this by trying to pass dry sand through a funnel; sometimes, the funnel stops flowing, as the grains are forced together and bind up, thus completely defying gravity. You have to jiggle the sand and/or funnel to get the sand flowing again.

[Colin Ibbotson]

“I'm still not sure of the logic of the bottom-fill. I'm not sure what benefit it gives over a conventional top-fill (other than draining, which could be done with a simple drain hole). I'd be grateful if you could explain the philosophy.”

Ultralight packs usually have a very simple draw corded top closure that rarely keeps out the rain. In addition any wet kit that goes into the pack (waterproofs/shelter etc) drains into the bottom and sits there. A sleeping bag is usually the first item in and even in a dry bag I would rather not have that sitting in water. You could fit a drain hole but the water would still have to run over all your kit before finally draining out the pack. My bottom opening pack allows for drainage and guarantees that the sleeping bag will not be sat in any standing water. As Derek stated water can enter through the skin at the strap openings. However, water can only get as far as the closed cell foam. What happens now is the water works its way down the pack between the skin and foam until it drains safely and quickly out the pack opening. A drainage hole just wouldn’t work as well. This system also allows me to access the contents without removing the rain cover and so saves time. After a over a years testing I’m convinced this is a far better method and keeps your contents drier than any conventional system.

Hope that Helps!

[Kevin Beeden]

Okay, thanks Colin.

Your logic is as I'd imagined; the draining issue. I'd figured that water could leak in through the slots, and leak through the non-waterproof skin, and pondered ways of trying to avoid this (without much success…). I mentioned this and drain holes in earlier posts.

I'd envisaged using a waterproof fabric for the upper valance, and a drybag-style rolled closure (simple, cheap, light).

> This system also allows me to access the contents without removing the rain cover and so saves time.

More so than a top-opening bag?

Given the lower-slung pack I'd envisaged, it looked like the upper CF rod and shoulder straps were going to mean a load suspension below useable pack space, which I thought could be filled with lightweight stuff I might need during the day.

The idea of having my wet tent at the bottom of the bag, rather than the top (last-in, first-out), and so not draining onto the rest of my stuff (esp. sleeping bag) is appealing, certainly.

Did you have any problems with the mat getting wet from inside the pack? The wet outer side can always face down when unrolled in the tent, leaving a (mostly) dry surface to sleep on. Or do you put your mat under the groundsheet?

[Author]

Posts