Down the Evazote rabbit hole and other load hauler pack questions

1. I used 6lb density minicell T600 from Foam By Mail and it worked great for my little kid’s pack belt and straps. I purchased 1/4” thick, using it as is for the straps (a lightweight pack), and laminated two layers for the hipbelt. This is the approx density recommended by Stitchback gear. I’d think it would work well for your purposes in a 1/2” thickness for the straps and belt, but for a heavier load, you are going to want to reinforce the belt with a kydex sheet, or some similar stiff plastic. I’d not go any lower density than that, as recovery and ILD is not as good for the heavier loads you want to carry. EVAZote is a great brand and if you can get it at a reasonable price, take it, but the Minicell is very serviceable, and I expect the T600 to work well for any pack needs.

As for construction, I favor a solid fabric facing my body rather than spacer mesh, mostly because I don’t like the idea of the mesh soaking up my nasty sweat.

Thank you for the reply and your experience Michael. Any feedback on the suitability over time? There are some comments about similar foam collapsing/losing thickness over time. Nunatak actually tested a whole bunch of Foam by Mail products to determine how fast(if at all) it would recover from compression and he didn’t rate the T200 well, but the T600 may be completely different. I’m not sure if he tested it.

https://backpackinglight.com/forums/topic/minicell-t-200-crosslinked-eva-2/

What did you use to laminate the 1/4” together?

If you look at the T200 vs T600 specs, you’ll see why T200 would not be suitable for something like pack straps or belts; T600 has 3-4x the compression strength, tensile strength and tear resistance of T200, and 1/4th the compression set of T200, but it does weigh 3x as much. Does weight matter more to you? Many people here, when trying to find foam to work with, seem to prioritize weight over the other useful properties of the product, and this is not a good way to go about designing a pack that needs to be reliably comfortable under load. I can’t answer for Nunatak, but I did have the discussion on this forum about his tests – I came to the conclusion his tests were not an accurate simulation of the use cases I’d be considering if I were designing a product. He has different opinions and probably different considerations, and that is ok. He also has access to Zotefoam as a business who can buy in large quantities (at least large by my MYOG standards) . You linked to the thread I created on the topic, so you have my opinions and reasoning to make a judgment for yourself on how to proceed. As I said, if you can get a hold of Zotefoam products for a price you are willing to pay, then get it, as it is higher performing product – it should be for 3x+ the material cost. I just wasn’t willing to pay for performance I didn’t think I needed. I guess time may tell, but I trust the product specification, and MYOG is a cheap hobby for me.

For laminating, I just used 3m77, no issues. Just make sure to rough up the surfaces a bit and give the surface a good cleaning with isopropyl, and you should be good to go, especially with the large mating surface associated with a hip belt. You need to spray both surfaces and allow them to dry a bit before putting them together and then hold them down under a little weight for the suggested curing time.

Regarding my experience with T200, I’ve used it for my sleeping pad system. I have a couple weeks of sleeping on it (in conjunction with my BA uninsulated AXL), and have noticed no deterioration in the functional properties. It has not accumulated anything except the expect scratches and dings associated with the normal wear that you would expect foam to have after throwing on the ground and sitting/laying on it. I suspect Zotefoam would “look” nicer since it does have higher tear/abrasion specs, but functionally I stand by my opinion that it would not do the same job any better than the T200 for me. YMMV

Thomas

I’d love an answer to the same question, as I’m also inspired by the McHale belt.

Do you have any info on the thickness of foam Dan is using in the Critical Mass? Maybe a McHale owner could chip in?

I might be able to help a bit with the density though.

I had a bit of contact with Zotefoams when I was persuading a UK retailer to duplicate the GG Thinlite Evazote pad.

Evazote is widely regarded as having better recovery and tear strength than the typical closed cell foam, which is presumably why Dan uses it. Zotefoams claim that there is still little on the market to match it.

I know for sure that the Thinlite is made with the 35kg/m3 density. I suspect that would be too light for this usage.

The classic Karrimat that pioneered the closed-cell mat market was made of the 45kg density according to Mike Parsons the inventor, who dropped in on a discussion here on BPL some years back.

I have a prototype Karrimat, and it’s still usable after over 50 years. It’s pretty durable stuff!

UK cottage maker Colin Ibbotson of Tramplite is an engineer and works to legendary standards. He used to use 45kg Evazote on his packs, but claims that it would sometimes compress if used for months on end on thru-hikes. It will last for decades if given time to recover between uses, but in his experience constant use is an issue for some. So 100 days of weekend use is different from 100 of continuous use.

Intriguingly, Colin claims he has found something better now, but he’s keeping that proprietary.

I think for most of us Evazote 45kg would be a pretty solid bet. I plan to make the belt and straps replaceable in case compression becomes an issue on a long hike.

I have a couple of historic Karrimats to cut up. But for others it might be hard to source, unless you could maybe blag some off a cottage maker. Evazote is tricky to make and expensive, so few retail foam suppliers carry it. Your best bet would be to find a genuine 45kg Evazote sleep mat, but buyer beware, most modern mats are not made to this standard. In particular the Karrimat trademark has expired and it’s become a generic name for any kind of closed cell foam mat.

Multimat is a trademark of Zotefoams. The cheaper mats use their inferior Plastazote, but the more expensive ones are genuine Evazote if you can source one. It would be quite an outlay, though, and might not be worth it…

I wouldn’t use foam with that low of a density on a pack unless a light carry, like 10-15lb. Do the math. 50-60lb spread out on the loaded surfaces of your hip belt and shoulders should not exceed the 50% ILD rating of the foam, or you will likely permanently deform the foam. If I was going to design the product correctly, I’d likely shoot for a max 25% ILD when the pack is loaded to its max rating.

Evergoods used Ev50 in the shoulder straps and HD80 for the framesheet in their MQD24.

The shoulder straps have a wonderful compression; they feel amazing to just squeeze in your hand. But they flex/bend with less resistance than the hipbelt on my ULA catalyst. I think EV50, or similar, would be amazing for cushion and hugging the hip bones, but may not have the resistance to deformation you want in a load hauler hipbelt.

The HD80 frame sheet has always returned to its curved shape, even after being slept on etc. Never felt anything poke thru. Definitely stiffer and able to hold its shape much more than the EV50, even though its thinner (if I had to guess the hd80 is 1/4-3/8″ thick and the ev50 is about 1/2″). It is hot against the back.

I bet you’ve seen this, but to me the most exciting aspect of using zotefoams for myog is that they publish tons of technical data on their products

https://www.zotefoams.com/downloads-category/numerical/

https://www.zotefoams.com/downloads-category/general-properties/

The EV50 does seem like it would be a good choice for that pack, as your experience suggests – it’s specs are well below that of the minicell T600, but it is lower density, so that is to be expected. It is a relatively small pack, and the lighter foam suits it. The HD80 also seems suited for its task as a framesheet. With a compression stress-strain of 593kPa (86psi), I cannot see you or anyone approaching the mechanical stress limit of the material by just laying on it. You might approach 2-3psi by standing on it – it would just pop back into the shape, as you say it has.

Michael,

Agreed about the avoidance of weight and compromising on characteristics that many people are doing. I’ve already got lots of light weight foam and several minimalist frameless packs. This pack is for heavy ropes, expedition gear, etc , I’m not that concerned about adding 50-100+ grams here or there if the performance scales up.

Any reason you went for the T200 or T600 instead of the heavier weight Cross-linked EVA in 2,4,6, etc pound densities? I’m just thinking that Evazote is also cross linked, so maybe those would be better?

I’ll be grabbing a can of that Spray 77 one of these days, thanks!

Geoff,

I do have access to buy those .5 and 1.5cm Evazote sleeping pads from MEC. How do you think they compare to the original Karrimat? You mention 45kg density a lot, but it seems that Evazote is mostly sold as EV50, which should be very similar I imagine.

I actually got off the phone with a local company earlier who was selling “Evazote” foam but it seems that their supplier was just pretending it was evazote and couldn’t pull any specs on weight or anything.

Jacob,

thanks for the experience with the EV50 from that pack. Have you ever handled a Seek Outside bag to compare? I really wonder what they use to keep their bag stiff. Maybe they laminate something like EV50 to a firmer thin foam.

I have actually tried using a very stiff 1/2” foam(interlocking floor mat) with a 1/4” softer foam in front and it wasn’t too great of an experience.

Then again, the man himself, Dan McHale only uses Evazote it seems, just a single density…I wonder what he uses and how think.

Any reason you went for the T200 or T600 instead of the heavier weight Cross-linked EVA in 2,4,6, etc pound densities? I’m just thinking that Evazote is also cross linked, so maybe those would be better?

I picked up sheets of T200 and T600. My intended use for the T200 was strictly for sleeping pads. I do believe there may be a place for the T200 in packs, but not in packs intended for heavier loads. I’d have to do the math though, before considering.

Minicell T200 and T600 are chemically cross-linked EVA foams; the T200 is 2lb density, the T600 is 6lb density. They are, chemically speaking, the same category product as Evazote foam. The difference is in the foam recipe and “baking” process. Evazote seems to have a better process than the manufacturer of Minicell if the required performance specs for your design call for that of Evazote foam. I selected the T600 for packs, specifically, because a similar density was recommended by Stitchback gear, a guy who sells MYOG pack patterns. I relied on that recommendation for pack making. I could probably get away with a little lighter foam, and that would result in a little more conformity to anatomy than the heavier foam, but it would be less supportive and robust. This is typically why professional packmakers, and also manufacturers of other foam products, i.e. mattress mfrs, seat companies (I work for an aircraft seat company so have a little bit of knowledge of this from work experience), etc, specify dual density (or more) layers in their soft product. Usually a relatively soft layer facing anatomy for comfort, and a heavier foam for support/structure.

I really wonder what they use to keep their bag stiff.

Many pack makers will laminate a thin plastic sheet to the foam to keep it stiff, either in the the frame sheet, the hipbelt, the straps, or any combination. a .04-08″ thick sheet of kydex can be used. Some makers, like Kelty, just sew the plastic to the outside of the foam, like the hipbelt on my larger kelty 80L bag.

Thanks for the information about the T200 vs T600.

I wonder if anyone is willing to apply a seam ripper to a McHale pack or a Seek Outside! I’m definitely curious about the thickness, dual density(or not) and other characteristics. I’m pretty sure that Seek Outside does not use a plastic stiffener, but I know my Mystery Ranch bag does use them, even in the shoulder straps. McHale specifically thinks they are a bad design choice, but I’m sure it all comes down to the higher density foam in the right place to make up for that lack of stiffness.

I think most use HDPE (high density polyethylene) not Kydex. Not sure what kydex is made of, but it is very heavy.

Thomas

I have both Evazote grades beside me now. I know for sure that the GG Thinlite is 35kg because I got that in writing directly from the sales guy at Zotefoams. It’s quite soft but still seems pretty resistant to compression. For example pinching it as hard as I can doesn’t leave a mark the way it would on a cheap foam. For a light pack you could probably make a decent belt economically by cutting up a GG pad and laminating it. For a load hauler, probably not wise?

The Karrimat is original and decades old. Likely they have changed the range a little and the equivalent is now the 50kg.

Digging my heel into the Karrimat with my full bodyweight doesn’t leave any kind of compressive mark.

I’ve had a 24kg /53lb kettlebell sitting on it for a couple of hours with no visible compression. A slight rim on the bottom of the bell left an indent that quickly sprang back. I can’t detect any difference in texture with my fingers between the uncompressed and compressed areas.

In my (half-century!) experience with Evazote, it’s very robust so long as the load is soft and distributed – such as a human body. It only gets damaged if the load is hard and focused in a way that wouldn’t occur in a pack. The only time I hurt mine was when I rolled it and bound it too tightly with thin paracord for a couple of years. It eventually recovered though, and I can’t see any sign of the damage now.

If you dig around his site, Dan is a great proponent of simplicity and comfort in hip-belts. He is scornful of the common approach of putting in a rigid layer. I have to say I agree – I tried one of the bigger Ospreys in a shop recently out of curiosity to see how it carried, and found the hipbelt very uncomfortable. It was too stiff and didn’t mould.

Personally, I’m going to give the Karrimat a try. I have enough for multiple belts, so can replace them if they compress, and I have it to hand. Also, it’s thin enough to sew through. But 40lbs would be a rare load for me, so my priorities are a bit different.

I think most use HDPE (high density polyethylene) not Kydex. Not sure what kydex is made of, but it is very heavy

I am sure. Just some cursory research on HDPE sheet vs Kydex (or “acrylic” as a category) sheet show a .034lb/cu.in. vs. .049lb/cu.in. , so not a huge weight difference in these specs given how much might be used in a pack, but I see what you’re saying. I’ve not seen a need for a plastic stiffener in my MYOG packs, so I’ve not done proper research on the type of plastics that are most used. I hope you will share your material selection journey for your design as you go through the process.

Geoff,

Appreciate the comparison of the GG Thinlite to your karrimat. I hope that the MEC Evazote is of similar quality, or at least is what I’m looking for with regards to my plan for usage. I was assuming that it is EV50, but have no real idea of what spec it is. Maybe it us 45 or 35 or something completely different.

https://www.mec.ca/en/product/0808-022/Evazote-Winter-Sleeping-Pad?colour=NOC02

Now I can do a little math. It’s 525 grams, 150 x 50 x 1.5 cm. So thats 11,250 cm^3 So it seems that it may be exactly like your Karrimat, as my math = 46.67 kg / m^3.

Hopefully it is as resilient as your original. Also 1.5cm is very thick, thick enough I feel like no additional thickness is needed. They also sell it in 0.5cm, which may be the better idea so I can adjust thickness with lamination, or make it dual density or use it for shoulder straps as well. Now can my sewing machine go though that much…

From my experience I think the HDPE is stiffer than kydex per gram. I bought two thicknesses of kydex sheets to use as frame sheets and quickly gave away the thinner one to a friend as it was far too flimsy to use as a frame sheet. The thicker one weighs so much that I simply have no desire to use it. I believe I had 1/16 and 1/8”. Not recommended.

Thomas

1.5cm is thick for an Evazote pad – never seen one like that! I don’t have callipers, but I think mine is 0.75 cm which was the standard for a Karrimat.

Looking at my other packs, I suspect that 1.5 is about right for the hips, and 0.75 about right for the shoulders. I may try a single layer, but otherwise I’ll have to laminate. I may ping Zotefoams for advice about an adhesive. Or I may just sew them together, on the outside chance that my machine can handle it.

I just took a close look at a pack I’ve literally been using since the ’70s on an almost daily basis. In fact I’m just about to head out with it now. The hip-belt foam is pretty compressed, as you’d expect, but still works fine for me at medium loads. I wonder how much compression is really a problem if the wrap is good and spreads the load properly over the widest possible area? One reason why I plan to make the belt quite wide – less pressure on the foam and less pressure on the hips at any specific point. And full-wrap, obviously, rather than wing.

I think some issues with compression can be addressed with designed, such as the width of shoulder straps. I have been making iterations of hanging belts, and many of my designs are greatly affected by the collapse of the foam on the vertical plane. For example I have two pieces of vertical webbing sewn with ~5 inches apart on the middle of the back of the hip belt. They’re sewn like daisy chains allowing a tubular frame to slide through them. This causes a lot of collapse and rotation of the internal foam. Seek Outside and McHale’s critical mass aren’t as affected by this issue because the belts are loaded below by webbing from the seam going 1/2-1” below and bolting to the frame. This creates other issues like having to have a taller frame which may rub while down climbing or glissading.

Here’s an idea for a Unaweep-type hanging belt without too much weight in the frame. Practical to make too. The maker says it’s a great success and works well with big loads. Very burly pack at only 3lbs (it’s for canyoneering). It could easily be made much lighter, especially if you simply put the vertical stays into sleeves for a simpler frame. He bought the belt off Seek Outside.

https://outlivingblog.wordpress.com/2015/03/24/the-big-ugly/

Yes I have ready that article extensively, that seems like a great design, very close to the McHale Critical Mass. You can actually see in the first photo some of the foam from the belt and it looks like it is dual density.

I have actually considered just buying a Seek Outside belt…but that would be cheating!

Have a look at the Rogue Panda Zoro (the pack has been temporarily discontinued, pending some changes) and the SWD Big Wild (not released yet, but the below link has some discussion and photos)

https://youtu.be/GckGMz1M8LQ

https://backpackinglight.com/forums/topic/superior-wilderness-designs-big-wild-70/

The Big Wild in particular has a very simple belt attachment that I think would be worth trying out. It has triglides on the bottom back of the belt, and webbing sewn directly to the internal frame channels just weave through those triglides.

I did not read the entire thread but I can comment on the t200 (2lb cross linked polyethylene foam) for use with shoulder straps:

I concur with the others and say within 1000 miles of use in a lightweight pack (25lbs or less) the 2lb t200 minicell foam has compressed considerably and does not have the necessary resilience for a load hauler pack nor a lightweight pack, imo. I used this pack for around 2700 miles and it worked but the compression of the shoulder strap foam was certainly noticeable. Would look into 4lb at least.

Thanks for the heads up on the Zoro – it’s not on their website so I’d never spotted the video.

I’m attracted by the idea of a floating belt, even though they’re generally associated with heavier loads than I’m designing for.

You get a pure full-wrap belt, which is obviously the ideal, and also a degree of freedom of movement that’s missing with any kind of more direct connection.

The weight of the cross-stay is offset by the fact you can dispense with the lumbar pad and (in most designs) the great slabs of velcro they use to attach the wings. And the Zoro shows that it can be unobtrusive and minimal.

The Zoro belt looks too narrow, though – and reviewers here on BPL seemed to agree. The zipless belt pocket closure design is potentially brilliant, provided it doesn’t leak.

The main takeaway from the Big Wild is the new strap from the top of the belt to the main compartment, which Ben says has transformed the carry. Another solution that simple and elegant.

I was a bit taken aback when Seek Outside abandoned the full-wrap belt for their Flight series – I was expecting a lightweight version of their successful Unaweep suspension. But following the thread that tracked the prototyping I think that may have been a marketing decision as much as anything. Making the belt adjustable means it can be fitted to a much wider range of customers and they don’t have hassles with sizing. The full-wrap belt is much less adaptable, but that’s not an issue with MYOG.

PS – so far as I can tell the Zoro doesn’t have a cross stay at the bottom. On the Reddit thread he say’s it’s a twin-stay pack. That would certainly simplify things and it’s lighter too. He says he spent 1000 hours developing it, so this decision won’t have been made lightly.

Do you feel the cross-stay is a necessity at the 40lb level, provided the bag is well packed?

That Big Wild idea of anchoring the belt off the bottom of the frame, then ‘loosely’ having it secured further up the pack may be a very good idea. It may mean that you can get away with far fewer structural components. Seek Outside attaches the webbing from their shoulder straps to the belt possibly for similar reasons. Or maybe just so the belt is held in a good position when donning/doffing the pack.

I too was disappointed by the Flight series packs. One immediate limitation I see is the maximum height of the frame. I’m 6’ tall, 19-20” back and a 24” tall frame is not good enough. They should’ve provided 26” or higher options. Dave C and others on this forum have already extended the frame height (required some sewing, such as moving the load lifters higher). I think that the above combined with a better hip belt / frame attachment it would be a great pack for load hauling. I bet if you just added two pieces of webbing into the bottom seam of the pack then anchored them to the bottom of the belt it would be great.

Also if you haven’t read this thread you should take a look, Nunatak is down the same path as us and has developed some great looking prototypes.

https://backpackinglight.com/forums/topic/myog-load-carrying-scrambling-pack/

He uses a horizontal stay at the base of the pack but does not anchor to it…its just to prevent barreling.

I do not think a horizontal stay is completely necessary but I think it depends on how you pack your bag and the distance between your body and the pack. For example, will the lumber pad, hip belt, etc create enough space that this barreling wont affect comfort?

Lumber pads are another point of contention, as most pack manufacturers have them, but Some have suggested a good full wrap hip belt without is better. Seek Outside sells them as an add on and suggest most people prefer them them.

One thing that the Zoro, Nunatak and McHale do is curve their belts upwards towards the buckles. This looks a bit strange but what it does is create a ‘conical’ shape, where the top is narrower than the bottom so the belt will naturally stay on the hips. I am definitely going to be doing this on my next hip belt. Interestingly Seek Outside does not seem to do this.

And another point of discussion is the friction of the belt to prevent it from sliding down your hips. McHale uses 500d cordura for the inside of his Critical Mass belts, most use 3D mesh. Hyperlight and Dave C uses inverted 3D mesh so that debris, pine needles, etc don’t get stuck in the mesh. I personally have been using this inverted method for a long time, but maybe I should try it un-reversed for additional friction. One thing I’ve noticed is the 3D mesh is much grippier in one direction. If the diamond shaped holes are longer horizontally it will provide better vertical friction, and this includes when reversed. Another thing I’ve seen on hunting and military packs is patches of ‘slip-not’ or gripper type fabrics on the lumber pad.

Here is another pack that may be worth checking out for inspiration. It hasn’t been released yet, but it has a single stay directly connected to a full wrap hip belt. It doesn’t seem to have a hanging hipbelt though.

https://www.swdbackpacks.com/product-page/Movement-35L-UltralightBackpack

It is supposed to be rated to 35-40lb without load lifters and this just seems like a fantasy…but I suppose if the belt fits just right and doesn’t slide down at all, maybe this would be possible.

Fun thread.

Here’s a pack I made last year, but had to put away in the chaos of getting the Bears Ears to market:

30 oz framed pack for medium loads and BV450

Not a load hauler per se, but with features pertaining to this thread. Take note it is not completely finished in those images, and many details likely will end up different. It’s 30 ounces and somewhat bigger than a HMG 2400, and the main use case is 3-4 day trips with a BV450.

Getting a ‘floating’ belt attached directly to the frame ends feel pretty good when carrying, obviously. I am concerned about abrasion to any fabric in between said frame ends and the ground, especially in canyon country down climb scenarios, so the frames are external and only tough webbing in two layers take the abuse.  Also the frame ends are up a bit from the actual pack bottom, again to limit their contact with rock.

The pack bottom is one piece of 1000d Cordura sculpted to shape via one short seam on either side. I found that seams running up the pack front from the lower corners will abrade quicker than smooth fabric. See pic with white pack. This was made with woven 6.5oz Melange with Dyneema, and the hard edge of seam binding on the inside quickly made a hole, despite only a quilt was stored there.

Thanks for he contribution! I’ve been following your pack designs very closely. Really appreciate the outside-the-box and creative solutions to problems and experimentation!

That hip belt attachment is quite ingenious…the Velcro will provide the vertical stiffness but will still allow all the weight to be transferred to the belt. I suppose you could always bring a few strips of Velcro to quickly add/remove the amount of hip belt freedom on the fly.

You’ve been going through some neat trial and error for the bottom construction of your packs. Some of your older ones had very neat patterning. This black one with just the two darts seems like a good design!

I have just been making my packs more simply: back panel attaches to bottom(which would be a more durable material like X50, bottom panel attaches to front, then the sides with pockets are sewn at the end. This creates those ‘sharp’ seams in the bottom corners, especially when I put water bottles in the pockets. While I’ve only been to Utah a couple of times (including some canyoneering) there is nothing I’ve encountered that is more abrasive than that slick rock in slot canyons!

I know you mentioned in another thread that you had laminated the outside fabric (in this case the black cordura) to thin 12lb foam(1/4”?) then to a softer foam, then 3D mesh or was it a stretch fabric…Do you mind going through the details of your current belt here? Especially specific products, as you definitely seem to be figuring this out!