I don’t expect there to be much interest in this pad system because it is a fairly niche item (and fairly heavy and somewhat bulky), but maybe some might find it peripherally and conceptually interesting, and since I’ve talked about it, figured I may as well share it though I’m not completely happy with how it turned out (it turned out a bit heavier than I had hoped/anticipated).
Concept (next post will have pics): Wanted a non air insulated and cushioned pad for very serious/extreme cold conditions (-30F and potentially significantly colder). Said pad needs to have very high R value for the weight and bulk. More importantly, it needs to be extremely reliable with no air leak type issues that are a potential issue with air inflated pads not even considering pressure changes based on temp fluctuations. Why not just CC foam? Mainly the bulk and I don’t find foam on a hard ground all that doable anymore.
Motivation: Goal or dream to eventually do an Antarctica trip if funds ever allow for it. Arctic trip would probably be cheaper, but I don’t want to have to deal with things like Polar bears as I don’t want to be lugging a rifle or copious amounts of bear spray (apparently they can be pretty persistent).
Solution: Primary insulation is based on vacuum insulation panels that are homemade/MYOG. Some insulation is provided also by a combo of the thin EVA pad that is underneath them, along with the strategically placed kapok filled “mini pillows” that are used for cushioning, and the “loft pocket” areas where a sleeping bag’s insulation would fill in some. Understood is that a thick sleeping bag, and not a quilt would be used with such a system.
Why vacuum insulation? Cuts down on bulk primarily, a bit on weight, and is the most efficient form of insulation. There are reports that vacuum insulation panels actually get more efficient/higher performing in very cold temps, which is unique to this form of insulation (for example there is an Alaskan group that put VIP’s in a house for testing and found the above to be true).
Why kapok? Light weight, inexpensive, highly insulating, environmentally sustainable, and more cushioning comfort than foam (kapok is commonly used as a stuff in natural cushion market etc). Pretty durable with compression cycles. Almost as light and insulating as lower fill power duck down, but resists compression more. Compresses more than foam, but not as much as down. Sort of a sweet spot for cushioning. What is kapok? It is a fiber grown in a seed pod of a tree that are short, pretty fine but hollow fibers that are sealed at one end but not the other. Also covered in a thick coating of natural wax which makes them highly hydrophobic. Before foam became widespread, kapok fiber was used in life vests, Arctic boots, etc because it is buoyant in water (more so when encased in a waterproof fabric/matrix), highly insulating, and highly hydrophobic. It is not used as a insulation fill in things like sleeping bags or the like, because it doesn’t compress down as much as down and it tends to clump more. Also not quite as insulating per weight and loft/volume as higher fill power goose down (more akin to 500/550 duck down). However, it is excellent insulation for smaller items like booties, pillows, etc. I’ve used a kapok stuffed pillow for a number of years now and it is by far my favorite pillow material.
Execution/implementation:
When I have made VIP’s in the past, I have used more “traditional” core materials such as perlite, fumed silica, and/or fiberglass batt (for homemade coolers/warmers). Fumed silica is the best filler/core material for VIP because it has a very high insulation value even when not under a vacuum and it is very light weight. It is very similar to silica aerogel in its weight and very low thermal conductivity (but far cheaper). It is probably the most commonly used material by industry to make VIP’s.
However, it wasn’t a good material to choose for this purpose because it is a somewhat fragile/brittle material and besides being under atmospheric pressure at a vacuum of 28″ Hg, it would also be subject to my body weight pressure and in an uneven way. Fiberglass batt would have been robust enough, but it is heavy. Perlite would suffer the same issues as fumed silica, and isn’t as good insulation wise anyways (thought significantly less expensive). None of these materials are particularly sustainable either (takes a lot of energy to make these materials). And fumed silica is fairly expensive.
I needed something that could take compression no issue, that was soft, with some give but also resists compression, was light weight, insulating on its own (in case any leak developed), reasonably priced, and hopefully more environmentally sustainable. This naturally led back to kapok–not just for the cushioning pillows, but also as a core material for the VIP’s. Because the fibers are hollow and sealed at one end, they resist very high compression, but while being soft, light weight, having some give/compression. A material I could roll around on with my body weight and not have to worry about damaging either the fill/core material nor damage the plastic & aluminum films it was encased in. The downside is that it does compress some vs a more stiff material like the ones mentioned above (especially fumed silica and perlite), which means you need to pack more material in, which does increase the thermal conductivity some.
Also, being a soft material that I had to stuff in there, vs pouring in a powder of stiff, evenly spaced material, it was also hard to get the thickness completely uniform. But the tolerance ranged from no less than 1/4″ of vacuum and no more than 1/2″ of vacuum. For the most part, I was able to keep it in that range (a couple spots were closer to 3/4″).
A typical industry VIP provides around R 25 to 30 per inch. Since I was not using the favored fumed silica, but kapok fiber primarily, it wouldn’t be that high. Probably more in the range of R 17 to 20 or so per inch (but this would need to be tested for more exact numbers). So some areas of these panels would be closer to R 5 and some R 10.
Then we need to factor in the few inches of the kapok fiber cushion mini pillows. When fully lofted, these are around 3 inches or so, but when laid on, compress down to around .5″ or so. This is around R value of 2 or so. For the “loft pocket” areas that the down sleeping bag would fill in, factor in similar (probably slightly higher).
Then the thin EVA foam pad with an IR reflector adds a small amount of insulation, and then the entire system being encased in a waterproof fabric on the bottom and a low CFM, but breathable material on the top would contribute a bit to the overall insulation. So I would guessitmate that at the thinnest areas of the pad, it would provide around R 8 and in the thickest areas around R 13.
Dimensions and general stats of the pad: I didn’t want a full pad. My lower legs don’t need as much insulation nor cushioning as the rest of my body, especially my core (I wear shorts most of the winter etc). CC Foam can be used for that. The pad is 43″ long and at the widest it is 26″ and at the narrowest part 17.5″.
Protection of the VIP’s: The thin EVA foam pad is primarily for protection of the bottom of the VIP’s. Gives them a little cushion from any potentially sharp, jutting, etc type conditions. Also to provide a lower slip surface. Then the whole system is placed in a fabric sleeve that has Mountain silnylon on the bottom and 1.7 oz/yd2 Mountain ripstop nylon on the top–both pretty tough fabrics for their weight. Course the kapok cushions (not to mention the thick sleeping bag) would also provide abrasion, cushion, etc protection too. But I wanted the whole system to be maximally protected from any potential punctures, abrasion, etc. When transporting the pad on a pulk or in a large pack, the VIPs would be stored in the fabric sleeve as well.
In the pics later, you will see that the VIP’s are kept connected both to each other and to the thin EVA foam pad with industrial strength velcro. Not shown in the pics, but the kapok cushions are also fastened/secured with industrial strength velcro to the VIPs (I took that pic before I had put those fasteners on). For the kapok pillows, I purposely used an uncoated 1.1 oz/yd2 nylon ripstop so that I could use the adhesive velcro (wouldn’t work with a nylon with DWR or silicone coating). Also, it was extra material/fabric lying around from a previous project and it works just fine for the purpose. Again, it is being extra protected by the bivy like sleeve that it all goes in, so didn’t need to be an especially robust material.
Weight…this is where I was a bit disappointed. I was hoping I could around a 4 or so lb system. For such a high degree of faff and worry free insulation, that is acceptable. But, it turned out to weigh 6.17 lb. Granted, this would probably be used with a pulk type system. But, I also realized (after the fact!) that if I thought outside of the box more, I could get the weight of such a system down significantly.
I have plans to build a truly UL cot that is an inch or so off the ground. Once you get off the ground, you need significantly less insulation. I expect the cot to be around 2 lbs. And while I don’t find foam all that comfortable on hard ground–I think that foam on a cot would be a different matter, so I will likely go with CCF as the insulation. I’m actually more excited by the UL cot idea/concept than I was about the above project.
(Btw, for a preview of the next project, it will be made out of a reinforced bamboo poles and polypropylene webbing primarily. The bamboo sections will be fit into lightweight and waterproofed wood or foam blocks, and the PP webbing will be run both lengthwise and width wise [around 2 1″ straps for length and 4 1″ for width. The bamboo will be reinforced with S glass grade fiberglass cloth, high strength epoxy, and/or kevlar tow/thread on the outside, and expanding closed cell foam [aka CCF] in the core. I have previous experience with experiments with such composites and they are VERY strong and very tough for the weight–often more than most carbon fiber poles, though not quite as stiff as the highest quality CF poles. As mentioned, thicker CCF will go on top of this for insulation, some for structure, and some cushioning. When I say the weight of the cot will be around 2lb, I’m not factoring in the weight of the foam pad though).
Pics in next post
