Hi, I’m currently working on a follow-up to my book ‘1001 Climbing Tips’, called ‘The Beyond: 1001 tips, advice and notions for mountaineers, expeditions and wild places’, the book being aimed more at a general outdoor audience, based on 50 years of trips. The book is not dry and technical, but more idiosyncratic, with lots of stories, but also some real nerdy, granular detail. I think there will be a big crossover into backpacking light territory, so I thought I’d post a snippet of the book to see what people thought. Hope you find it interesting, and at least one thing you find worth the read.
Padology
The old camping saying: “One blanket under you is worth two over you,” makes sense to anyone who’s spent the night on a deflated pad or been benighted without bivvy gear.
Nevertheless, the importance of padology, the science of insulating your body from ground conduction, is often overlooked by mountaineers, the main focus being on what goes on top.
The first principle of padology is that your pad, mattress, cot, or camp bed—whatever you use—reduces, or better, eliminates, conductive heat loss between your 37°C body and whatever you lie upon: summer grass, hard granite, or frozen Arctic Ocean. Yes, it’s nice to have something soft beneath you, but comfort is only a secondary principle, since even a feather bed will be uncomfortable if you’re cold.
A good example of conductive heat loss is a cheap blow-up air mattress, the kind you slept on at friends’ sleepovers. You’d imagine it would insulate well, but it doesn’t. Yes, it’s comfortable—20 cm thick, leaving you on a 500-litre cushion of air—but it’s also cold. You might have the thickest duvet on top, yet still wake up cold. The reason is that although air is often described as a good insulator, works best when trapped. Closed-cell foam (EVA) contains billions of tiny bubbles of air; your blow-up mattress only has one. These mattresses are just for comfort, and if you also want warmth—or at least to avoid the cold—you need to add a blanket underneath to insulate you from that big bubble of cold air, that blanket creating billions of little air pockets within its structure.
Now, fill that air mattress with something like open-cell foam, synthetic filaments, or feathers, and you trap the air within those cells and fibres, turning a single air space into millions. Once trapped, you both create a buffer between warm and less warm, which will slow or stop heat loss.
Although early mountaineers carried metal beds and sprung mattresses on expeditions, modern ones don’t want to carry thick PVC mattresses, so the depth, construction, and materials used have been refined over the decades. With the right insulator, you can lie on a glacier comfortably, swapping a 20 cm mattress for a 2 cm pad. For mountain padology, we can divide pads into two types. The classic pad is made from chemically blown ethylene-vinyl acetate foam (EVA, aka Ensolite or Karrimat) that is formed into sheets containing millions of 0.05–0.2 mm bubbles of air. You can burst them, but it will take you some time. The other type is what is commonly referred to as a self-inflating pad (SIP), even if they don’t self-inflate, but are pads with an inflatable void filled with some form of air-trapping filler, be that foam, fibre, or down. These feature much larger air pockets (~1 mm) that fill with air when inflated and empty when deflated. Neither is better than the other.
If under-insulation is only a matter of comfort, go for a SIP, and if weight and bulk aren’t an issue, make it full-length (~200 cm long by ~60 cm wide) and as thick as you can (≥ 7 cm).
The difference between ‘thin’ SIPs (~2 cm) and ‘thick’ (≥ 7 cm) is that the thin pads only insulate you fully when you’re lying on your back, while a thick pad should still maintain adequate insulation when lying on your side. Needless to say, a 100 kg man needs a thicker pad than a 50 kg woman.
If your life depends on your under-insulation, use an EVA (aka Ensolite) foam pad, as EVA is like the undead, being invulnerable to anything but fire; you can literally tap dance on your pad in your crampons, and it’ll keep on insulating. If weight and bulk are less critical than insulation, make it full-size and optimal thickness, which in EVA is between 12 mm and 14 mm (5-season).
If you want both comfort and robust insulation, use a two-pad system, with a full-length (or three-quarter) SIP and a full-size 4-season EVA pad underneath. You can use a very thin (5 mm) EVA pad to act as a robust buffer against the ground. However, by making both full thickness, you can use the EVA pad in places where your SIP would not survive for long.
If you employ a 4 mm EVA tent underlay, you could forgo the EVA pad in the above system, but if your SIP goes flat, you will be forced to cut up or fold the underlay to give you a working pad, robbing your tent of its extra warmth and utility.
Although most EVA pads are smooth, some are not—most notably RidgeRest or Z Lite style pads—which feature either horizontal ridges and valleys or cups like an egg box. The textured surface helps the pads’ insulation by cutting down surface contact with the ground and lets a thinner EVA foam match the insulation of a thicker pad. But mostly, it just makes the pad softer. The problems with these pads are the extra bulk, and that when you put them straight onto snow or wet ground, a lot of the benefit disappears, as the voids just fill with snow or mud. Another drawback is the simple advantage of a smooth pad—you can wipe it clean of snow, dirt, or spilled water in seconds. With a textured pad, you can’t, which means snow stuck in the valleys melts and soaks into your sleeping bag. For these reasons, this style of pad works best inside a tent.
If weight and bulk are more important than survival, such as on a fast-and-light climb, then use the lightest three-quarter SIP (~330 grams), but have a back-up plan in case the pad becomes punctured. I’ve generally found that the stress of worrying about my pad night after night makes any comfort gain not worth the price, and I typically only go this route when I know I’ll be camping on snow or if using a bivvy tent.
On scrappy bivouacs, where you might end up sleeping with a granite spike up your arse all night, or wearing all your rack, or even your crampons, with your sleeping bag pulled around you, a SIP has all the utility of a chocolate Jetboil. It’s just not robust enough. Another advantage of an EVA pad is its ability to conform and stick, allowing it to stay in place, such as wedged between rocks, when measuring comfort. A SIP, being slippery and full of air, won’t do this, making it unsuitable for anything but flat ground. You will notice this most of all if forced to chop out a ledge from snow and ice and then try to lie there for the night. An EVA mat tends to stay in place, whereas the SIP will do all it can to escape you and the ledge (if you can keep it there, a SIP will be more comfortable, but only if you can wrangle it into submission).
On the worst kinds of bivvies, you’ll often find yourself sitting (or standing!) and be forced to use your pad like a chair, lying back or sideways on the upper part. Try that with a SIP, and it’s like balancing on the edge of a slide; this is why a good scrappy climbing pad needs multiple attachment points to keep it in place.
The one advantage a SIP has over EVA pads on poor ground, where it’s lumpy and irregular, is that due to their greater thickness, they level everything out. I’ve spent several nights on ledges we’ve made somewhat flat by creating an ‘alpine patio’ out of rocks, which would have been grim to sleep on with a 1 cm EVA pad, like a bed of nails, but which was like a feather bed when using an 8 cm thick SIP; this is why an EVA/SIP combo works well.
As outdoor people, we tend to ignore PU (polyurethane) open-cell foam, as it’s bulky, heavy, and moisture-absorbent, but if weight and bulk aren’t an issue, perhaps at a fixed camp, and you can make up a waterproof cover from a soft, quiet, waterproof fabric, then it’s as close as you’ll get to sleeping in a bed. If you want real luxury, there are companies that can cut memory foam to size, matching it to your other pads. Due to its greater compressibility, avoid any foam less than 5 cm thick.
If you want comfort and insulation, and your life depends on it, and you’re going to be out for an extended period in a hostile environment, then go for two 4-season pads.
On the issue of setting fire to your pad, remember that EVA stands for ethylene-vinyl acetate, a copolymer that burns easily and produces fumes you do not want in your lungs or bloodstream. Beyond what burning EVA does to your lungs, it also turns into a napalm-like goop that will stick to skin and keep on burning. You’d imagine it’d be hard to set fire to your pad, but seeing as lots of people burn up in their beds, it’s not. I once set fire to the edge of my pad when it snuck into the stove flame, probably due to complacency after lying next to the stove for a week in a snow hole. The fumes it gave off were demonstrated by the thumping headaches we suffered as a result, not having the luxury of moving to other accommodation [Note: you can buy fire-retardant EVA from cosplay suppliers, handy if you want foam to back a stove board or line a kitchen area.] You should pay close attention to where your pad is when priming stoves to avoid ignition. Oh, and SIPs also burn, but with fewer toxins.
The one advantage heat-wise with an EVA pad is that you can set hot pans on them with less worry than with a SIP, as one might melt a little bit, while the other will just burst (good luck repairing a hole the size of a frying pan with a patch the size of a chewing gum wrapper); this also applies to tent groundsheets, sleeping bags, etc. If you don’t have a stove board or a small alpine cutting board, your EVA pad will likely serve as your kitchen worktop.
When searching for an ultralight way to insulate yourself from the ground, when 300 grams is deemed too heavy, people have experimented with some wacky solutions. One of my favourites was the balloon bed, two gossamer-thin layers of nylon that held several sausage-shaped party balloons, weighing in at around 80 grams, sans balloons (you had to carry enough for each night). This option required real skill and Zen-like stillness to avoid popping balloons, which would not only wake you up, but everyone else in camp. Another was to just carry enough pieces of EVA foam to cover your hip bone and shoulder, inserting these into your clothing so they stayed put all night (as long as you also stayed put). Then there was also the option of stepping down the thickness of your EVA mat by two-thirds or more, going from 12 mm to 3 mm, then making it half as long and tailoring it to your hip and shoulder width. Then there was a period when people thought a sheet of bubble wrap was the answer, which, even if you could not sleep, gave you something to do. In the end, I think people shook off this madness, as they realised that of all the things you can do without, or with less of, in the mountains, especially in a race, sleep was not one, and 300 grams was a price worth paying.
If you’re sharing a small tent with a partner, it’s crucial to avoid gaps between your pads; this will create a cold spot that compromises shared warmth and also form a crevasse for you to fall into. To prevent this, make up two straps, each in a figure-8 shape from 12 mm grosgrain ribbon, with a tiny, flat centre-release buckle on each loop of the ‘eight’, allowing the pads to be locked together securely.
Pretty much all SIPs are slippery, while all EVA pads are ‘sticky’, so lying the SIP on top of an EVA pad helps it stay in place, which is handy if you want to keep two pads side by side in a tent.
If weight and robustness are more important, perhaps because you have to bivouac in spiky places prone to bursting an air pad, such as ledges covered in shards of granite or pointy limestone, or in the woods, where the ground is covered in thorns and brambles, use a cut-down 3-season (~8 mm) foam pad, cutting it to span your shoulders to mid-thigh; this can be rolled up and secured to the pack, or you can cut it into three or four sections and tape them together with duct tape. To create a concertina pad, you need to alternate flat seams and folded seams.
The Swiss company Exped used to make an expedition pad cover made from EVA foam, which you could slide your SIP inside, creating a SIP sandwich, with 5 mm foam on either side; this protected both the SIP top and bottom and also provided a 10 mm EVA (5 mm + 5 mm) pad in case your SIP went down. Now they just make a plain nylon cover, as no one really understood how good it was. But you can sew one up yourself very easily, and it is ideal for extended expeditions. You can add further utility by adding toggles on the sides, allowing you to connect with another pad.
The importance of under-insulation means you always need a backup plan, either one you’ve built into your kit or by improvising something. The best built-in approach is to make a folding 4 mm EVA bivvy pad that fits into the back panel of your pack (some packs will come with one fitted, but you can usually make a better one). Due to its narrow width (30 cm), you generally have to sleep on your side to make it work, or use it as part of a makeshift pad. If you want to take it further, you can make up a bivvy pad using a combination of EVA thicknesses, having thicker foam for your arse and upper back.
One advantage of having an EVA pad is that it can be cut into two, helping out your partner if they find themselves without a pad. If you have a three-quarter pad, this guarantees that both of you will have a bad night’s sleep.
I’ve had to make do with a non-pad bivvy many times, and it’s usually not as bad as you’d imagine, as long as the ground is not frozen. Remember, sleeping pads are a modern invention. Humans have slept on the ground for millennia, so consider copying this approach by gathering flora, leaves, sticks, grass, and newspaper to create an ancestral bed.
I remember my grandad telling me how, before pads, you’d always dig a hole for your hip bone, as you had to sleep on your side to stay warm, as this created the smallest area of ground contact (when lying).
If your sleeping bag has a synthetic fill, it will provide some degree of under-insulation compared to a down sleeping bag, especially if you don’t have a pad. Although people would generally use a folded blanket as under-insulation in the past, the high-tech, pre-EVA/SIP pads were made from a fibre fill, like kapok, which most people now call a futon mattress (you can still buy fibre-filled pads, such as the Wiggy’s Ground Pad, which, although bulky, are very effective, warm, and indestructible).
If you can limit your ground contact to a minimum, you can use other kit to insulate you from the ground. The primary one is your pack, as both the back panel, straps, and belt tend to contain EVA foam, which generally goes under your body. Spare clothing, mittens, socks, and even packets of food or a folded map can go under your arse. If you’re climbing, you might also have a rope that you can use to snake across the ground and form a pad, as well as a padded climbing harness, chalk bag, slings, etc. A climbing helmet, when worn, also helps, as it keeps your head off the ground. As you can imagine, having a 4 mm foam pad in your pack makes this much easier.
What happens if you have no insulation at all? The most crucial thing is to adopt a position that minimises your contact with the earth, something most easily done by not sleeping at all and just keeping on keeping on. If you have to stop, don’t lie down if you cannot find any insulation. Instead, just sit and hug your legs. (If you lean against something, you’ll get colder quicker.) If you have to go prone, then either lie in the foetal position or kneel, so just the bony parts of your body are in contact: feet, knees, and elbows.
If you’re using a SIP, you must have a small (7 g) tube of sealant, like Aquasure, Aquaseal, or SeamGrip, and some waterproof fabric, such as a square of silicone nylon, or the repair patches you get with air pads. To repair, coat both the fabric and the patch, wait until it becomes tacky, and then stick. It needs to be left for about eight hours to really cure, so this isn’t a repair you can do in the middle of the night, although you can make an emergency repair (if you can find the leak!), let it cure for half an hour, and then just hope it’ll stay, and then overlay a larger patch in the morning.
If you have no repair kit and your pad is leaking, and you have duct tape, then a workable repair can be made by heating the sticky face of a tiny patch of tape (2 cm x 2 cm) over a stove and then placing this over the leak. Now repeat with a larger piece (4 cm x 4 cm), and once more with a full square of tape; this should work as a short-term repair.
It’s fine to blow into your SIP most of the time, but it should be avoided in sub-zero temperatures, especially on prolonged trips. The reason is that you build up moisture in the insulation that turns to ice once you’re no longer sleeping on it. Do this repeatedly, and you’ll end up with a significant amount of ice inside your pad, which can undermine its insulation value and lead to damage, such as delamination. If you suffer from this issue, your only remedy is to sleep on the pad and so melt the ice, then open the valve and quickly roll the pad up towards the valve, forcing at least some of the water out. The best way to avoid this issue is to use some form of pump, and most SIP either come with a stuff sack pump, or can accept one as an accessory.
All sleeping pads should have some way to secure them, as they’re very easily blown away. With an EVA pad, it is simple: just make a hole in one corner, thread some 4 mm cord, and tie a loop. This loop can also be made from 4 mm bungee and sized so it can wrap around the pad and keep it rolled up. With a SIP, you will need to add a loop around the valve using 2 mm cord.
People often assume EVA is waterproof, which it is, and therefore leave their pads exposed on the side of their packs; this can lead to bringing a wet, and often dirty, pad into a dry tent. For this reason, I usually make up a pad cover for my pads, so they remain pretty much dry, or snow-free, once they go into the tent; this is also one reason why SIPs rule for general tent camping, in that they remain dry.
Climbers usually store a rolled EVA pad on the side panel of a pack, the side straps being the obvious way to secure it. But on technical terrain, where you might have to squeeze through small gaps, it’s better to place it on the back panel, leaving the sides clean; this can be achieved using extra straps or a 4 mm bungee, ensuring the bungee crosses over the pad at least four times.
If you’re using your side straps to hold a pad, ensure they’re long enough. Being short-changed means you’ll have to fiddle with buckles and straps, leaving you short. If in doubt, make your straps longer and quick-release them to make adding and removing them easier.
A great little modification you can add to your EVA pad for tent-bound days is to draw on a chessboard, or a Go board, or Monopoly, or whatever rocks your boat. If it’s a chessboard, make it oversized so you can use random items as pieces.
To pack a SIP, open the valve, fold it in half lengthwise, and then carefully roll it up, expelling the air. Now, close the valve, roll out, and repeat, but this time really gripping the rolled-up pad as you go. When you’re close to the end, you’ll see all the extra air you’ve forced out, so now you can open up the valve and let it out, closing it again so the pad stays as flat as a pancake.
SIPs come rolled up in a nice little stuff sack, but often, this is just to make them easier to stack on a shop display, and often, you’re better off going for a ‘flat pack’. Roll out all the air, then fold the pad into a rectangle. Insert it down the back panel of the pack or into a square and layer it flat within the pack. This way of packing a pad is ideal when using ultra-light three-quarter pads, as it also affords them more protection from crampon and axe points.
A great way to evaluate the quality of your pad is when camping on snow or ice. If you wake up and find there is a perfect mould of your body in the ground, then that’s a sign you’re wasting heat. Often, when sleeping on snow with partners, you can really see who has the best set-up when you break camp.
The worst thing that can happen when camping on ice, which is generally found when bivvying under winter or glacial boulders, is for your substandard pad to result in the ice melting under you, leaving you in a pool of water, which will invariably find its way inside your sleeping bag (this would result in the problem being solved, as now you’ll have no body heat to spare). To avoid this, you either need to get a better pad system or, in the short term, try to boost your insulation by sleeping on spare clothing, your pack, etc. You can also try making a bed of flat rocks to lift your pad off the ice. Although this might not add to your comfort, it will be warmer and prevent you from waking up feeling like you’re adrift.
