Z-lite pad as pack frame – help needed

[Jan Rezac]

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[Jan Rezac]

I’m considering using a z-lite pad as n internal frame for a backpack. It could be folded so that one or few layers will be at the back, and the rest of the pad will be folded on the sides. This way, the center of gravity will be kept close to the back, and the sides will provide additional vertical stiffness.

However, I do not have the pad yet, so I’m reaching out for help here. Could anybody measure the dimensions of the configurations outlined below and post them here, please?

It is possible that none of the options will result into useful pack dimensions. In that case, I can always use a plain foam pad and score it so that it will fold the way I need, but ‘d prefer designing the pack around a readily available pad. Also, the z-lite provides more padding in less volume than flat pads.

I’d need the outer dimensions X and Y of the shapes A, B and C. Additionally, for C, I’d like to know also the thickness T of the three layers of the pad.

[James Marco]

I have used a CCF as a frame for about 20 years or so. Some with plane-jane blue pads, some with inflatables, mostly with NightLights and Nunatak’s Luna pads. Some have been internal mounts as you show, some wrap-arounds, mostly with external pad keepers… either sewn in custom or as on Gossamer Gear packs (pre-installed pad-keepers.)

Inflatables don’t work very well. Unless they are inflated rather rigidly, they do not have enough support. Even a torso length Xlite will be a full 4″ thick if inflated rigidly in a pack. It just takes up too much space to be very useful. For a brief period of time, GG marketed some pads (ibeams or something) that worked slightly in their pad keepers. But even these were not as good as a CCF pad. The prolights failed to support at all. These didn’t supply enough air volume, nor enough regular foam for support. The Z-Rest pads have too many segments to supply good support, though these work as well as blue pads. With a little planning to nest the interlocking “humps” of the older Nightlights/Luna pads, these worked best, by far. But GG dropped the older full length pads. The Luna (Mt. Washington) pad is currently the best choice, overall.

You hit problem directly with the sizing. The Z-Rest pads do not fit in most packs. The width of the internal width of the pack body can vary a lot: between about 17″ and 10″ depending on what pack you have. The height is usually correct at ~20″, but this can vary a bit. For the width, this can present a problem. Only a couple widths will work for the Z-Rest style pads to work effectively. IFF you have a hollow corner, there WILL be a tendency to stretch and/or rip the pad from internal stuffing. This will cause later problems while trying to lay it out for sleeping. Depending on which way the “fan-fold” is lined up, it can cause the fold to work backwards, though this is not a major problem. Sometimes the internal length can be a problem. Most packs have some sort of fold over lid (roll top, fold over, etc.) But, right after a resupply this can be a problem if you have extra in your pack. The pad can slip up and loose support/padding.

Assuming you get everything lined up in the pack, the overall configuration will be a boxy shape. It works fine in the pack, but this does not conform well with your back. Even with external frames, they apply extra padding (usually at the small of your back) to avoid this or pre-bend a frame to approximate your back. Internal frames are no different. These are usually formed to match the contours of your back. I remember several discussions about how to bend these to match various differences between people and is one of those items that really needs to be customized between each person. What you DON’T want, is a box against your back. Indeed, some packs are designed with a curve in them to match your back. (https://www.olympicul.com/)

The good news is that there is roughly a “square” gap up to about an inch that is fine to sleep on. This means that roughly up to an inch or so, the width between panels of a pad doesn’t really mean loss of comfort. Most contouring can be done within that inch. So, there is nothing that says you cannot slice the pad, add a 3/4″ gap of tape (duct tape or the like) between these corners. This lets the pad conform to your back (depending on how you load your pack.) OK, but now you need to load the pack in a specific order…and your gear needs to be a specific size… well, there are problems with is approach…anyway, not recommended.

Let’s look at the ergonomics of walking for a moment. Assuming, that the three panels are rather rigidly joined, you find that a walking motion will tend to torsionally twist the box you have created. This means you will tend to lift one side of the pack for each footstep. I really don’t think this is what you want. The load of the pack will alternate from one shoulder to the next…likely painfully after 10-20mi.

The torsional twist is a part of walking and cannot be avoided, but you do NOT need to lift half the load of the pack onto your shoulder with each step. The fabric of the pack, any looseness between elements in your pack, and compression of the pack should allow this without you lifting the entire weight onto one shoulder. Indeed, I don’t use compression straps at all. You really DON’T want a box shape. Rather a smooth transfer of supporting force onto your hips as they rotate for each step with little or no weight transferred to your shoulders while hiking. This leaves your arms and shoulders free for other tasks, balance, handling a hiking staff, and scrambling for some examples.

The best arrangement I have found is to simply fan-fold the pad, flat, against your back. This supplies support in the UP/DOWN direction (where you want it), adds a little resistance to torsional movement, but does not amplify this effect with weight in the pack as a box does. With a solid mount on your hips, 70% of the weight goes on your legs (where it ends up anyway) rather than on your shoulders. You end up with a slight bit more stress on the shoulder straps by increasing the distance from your center of gravity, but this is easy to correct by simply shifting weight more over your ankles rather than bending at the hips…maybe a half inch or less (10-15mm.) Only with full-on climbing with a 30pound pack has this type of loading ever bothered me.

Of the ones you have outlined, that I have used, they were made of the wally-world blue pads. These have an unfortunate tendency to curl. but can be “trained” to lay flat with a little heat. Generally, after cutting segments, they can be placed in a dryer for 3-10 minutes (depending on your dryer) and laid out against the curls or flat with some weight for an hour or so. That will remove the majority of the curl. No, an iron does not work as well… Anyway, I recommend you pick up a $10 special at WallyWorld to try it out, first. These are very easy to work with, an electric knife makes cutting a breeze, or, you can simply use a good sharp pocket knife. Then a length of duct tape on opposite sides for the fan-fold. Nightlites/Luna pads require a bit more. but are not too bad. Use a good carpenters square. You will find that CCF pads are not usually cut quite right. You will find that the Nightlite/Luna pads will “lock” together supplying about 1″ of supporting foam for every two layers.

The caveat with using pads as frames is that the tops need to be supported along the entire upper edge. A single center strap or a couple in the corners does not do it. It simply embeds into the foam or allows the foam too much movement to support the pack. And, the entire pad needs to be fairly well pinched together into a single support unit with Velcro, tight elastic or well sized pockets. If you allow it to slip up or twist sideways in the pack, IT IS NOT SUPPORTING the pack. If it buckles, it is not supporting the pack.

Try out a few designs. I would be quite interested to hear how you make out!

Anyway, the 3/8″ Blue pads have an R value of about 1.0 and weigh about 10oz (torso.)
The 3/4″ Luna pads have an R value of about 2.5 and weigh about 8oz (torso.)
The 2.5″ XLight pads have an R value of about 3.2 and weigh about 8oz (torso.)

[Aaron]

I assume you’re using a full length pad.  Consider cutting it in two pieces.  Use one folded flat 2 sections wide against the back panel for your frame, carry the other outside your pack as a sit pad.  Depending on how tall you are, you might not need all the sections anyway.  When you sleep, simply lay them both out – those pads don’t move around much. You could also add snaps or velcro tabs if you’re worried about shifting gaps.  I don’t have a new z-pad to measure for thickness, I only have sections of old pads that are squished and compressed, but the width folded 2 across is about 10.5″, and that’s how I’ve always carried them in frameless bags.  You don’t need to overthink it too much.  The key to creating a “frame” in a frameless pack is how you pack and compress the overall load, the sleeping pad is mostly just padding and helps create form. 2 or 3 folded z-pad layers will suffice for a padded frame sheet, but won’t in itself create much of a rigid frame.

[Edward John M]

What I use won’t work any more because it seems nobody makes rectangular short pads any more.

I simply took my 3/4 Thermarest and folded it in quarters and used it to replace the CCF and aluminium stay frame in my winter day pack. Not perfect but it works well enough up to about 10 kilos

[Jan Rezac]

Thanks for all the input. I should have clarified few more points:

• I’ve made multiple packs in the past, and I know exactly what I want to try this time. I’s an experiment, not an all-round pack for general use.
• It will be a small pack for light loads (weekend trips), so the purpose of the “frame” is more to give the pack a shape and to provide some padding than to transfer a load.
• I want the pad to be stored inside the pack also because I want it to be very streamlined on the outside.
• Now, for this kind of trips, I use mostly a simple small pack where I roll a CCF pad around its circumference. I plan to have an additional zipper opening in front of the pack, so this won’t work any more – I want the pad to form a wide ‘U’ instead of O, so that I can access my gear through the zipper.
• I hope that a folding pad will allow me to shape the pack better compared to the tubular shape one gets with a rolled pad.
• If the z-lite wont have the right dimensions, I will take a plain CF pad and add fold lines (scores + reinforcement tape on the other side) that will make it fold exactly how I want it. The advantage of z-lite, if it fits, would be a better insulation and more comfort for the volume it occupies.

[Lester Moore]

If you’re up for an experiment, you could test out what James mentioned above: cut the Z-lite into segments. If your pack has the usual side panel shape that’s thicker at the top and narrower at the bottom, then cut the pad into multiple trapezoidal shapes that match the combined shape of your back panel and both side panels, leaving the front panel and zipper open. You could add tabs to the ends of the segments using contact cement, grosgrain ribbon and hook-and-loop to hold the segments together for sleeping.

[Kevin Babione]

I think the issue is that the OP is not in this country and doesn’t have a Z-Lite to get the measurements he’s requested.

Jan – If nobody gives you the measurements in the next couple of days I’ll post them when I return home and can grab my Z-Lite.  Would you prefer inches or centimeters?

[Jan Rezac]

Kevin – thanks for the offer, that’s what I was looking for. However, it’s not needed any more.

I finally had the opportunity to stop by in a store where they had the pad at hand and measure the pad myself. It seems that I can fold the pad just the way I wanted. The variant C) pictured above is 34 cm / 13 inches wide, and that’s the width of the backpanel of my larger backpack I’m happy with (for a reference, I’ve just posted about it here). The pad can be compressed a bit, so I think I’ll target for pack width of 32 cm / 12 iches. It may be wider than what’s usually used in packs of this size, but that’s exactly what I want. There will be no side pockets, so the overall profile of the pack does not exceed the width of my shoulders/torso.

The volume for gear (without the pad) is planned to be 20 liters (+ some extra in extendable collar), what would lead to a pack depth of 18 cm / 7 inches if the pack was rectangular box. I think these are nice proportions, and it is close to what I imagined.

I will post how it turned out (but it may take some time).

 

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