The permaflate - general description

What we are trying to do with the permaflate, is make something better to sleep on when camping. Comfort and as much height above the ground as possible are provided by an airbed, but conventional airbeds have won themselves a well-deserved reputation for leaking. An airbed insulates better than most campers believe, but not well enough for winter use. Finally, if an airbed does fail on a very cold night, you are on the ground, and in deep trouble.

The permaflate uses a very light nylon mattress sheath with six individual tubes pushed into it. Provided you can insert the tube stoppers, this assembly does not leak, and we have yet to encounter a puncture. We will post you a single tube for testing if you are sceptical (see Read me First).

If you put a length of closed-cell foam between yourself and the airbed, insulation improves. If the foam is top-quality EVA, and half an inch thick, any catastrophic airbed failure leaves you still insulated if uncomfortable. In addition, any loose pile of gear that you sleep on undergoes a terrible transition during your night on the floor. The mattress goes one way, the pillow another, and any ancillaries to the far corner of the tent.

The latest permaflate allows a short section of closed-cell foam to be loaded into the airbed, where it does not move around. Even partial airbed failure has yet to be encountered, but in the event of total airbed failure, with the closed-cell foam installed, you will be deposited on the ground, lying on the foam with the pillow and buttock pads still functional. It won't be a nice night, but you will survive. You may provide any foam you wish, from bargain-priced Oriental upwards. Since the foam length is short, I personally use a top-quality half inch thick material, which provides excessive insulation until the night really cools off (minus 20 degrees Celsius). I would not even spend a night on this by choice without the airbed underneath, but it is tolerably comfortable on its own.

The channel mat

Half inch (12 mm) foam fits a critical industrial requirement, and consequently costs more. The foam material is cross-linked EVA (polyethylene vinyl acetate), which is more rubbery and heavier than the cheap polythene closed-cell foams. Rather than cut-sheet foam, I personally use a moulded mat patterned with two sets of channels running at right angles to each other. The result looks like a large slab of chocolate with each individual block being one inch (25 mm) square. The intersecting channels between the blocks are 5 mm wide, the mat thickness under the channels being only 4 mm.

Half inch cut-sheet foam cannot be rolled easily. The channel mat is more flexible, due to the thinner foam under the channels, and can be rolled as tightly as a 6 mm foam sheet, although the resulting bundle is of course larger. The moulding process forms a glossy, leathery 'skin' on each side, which is resistant to indentation and surface tearing. Water, which spreads over a cut-sheet surface, will not wet the channel mat skin and can be shaken off. You can stand, or kneel, on this mat without it going flat at the pressure points.

Practical camp-testing has shown up a feature of the channel mat that may be unique. The writer spent a night on fresh snow which began cold and dry, and ended warm and foggy as the cold front moved on. This produced a damp tent, and a damp synthetic sleeping bag. The next day there was no chance of drying out the bag, and the next night was clear and still, with the temperature dropping to minus 15 Celsius. I removed the flysheet to increase ventilation, and freeze as much of the sleeping bag moisture as possible onto the walls of the tent. By morning, as expected, the tent walls were generously iced, but I found on sliding the channel mat out from the top of the permaflate airbed that there was a siguificant amount of water sitting in the channels. This water had been pumped downwards by body heat from the sleeping bag before condensing in the channels. Channel depth prevented the water from contacting the sleeping bag and soaking back in. We do not yet know how often the channels will collect water under a sleeper, but when your bag is damp, any additional means of drying it out represents an advance. After a few more cold camps, we can say on any night below about minus 5 Celsius, once your bag has had one night to pick up moisture, water is pumped out of the bag overnight and collects in the channels.

The permaflate is designed to minimise the length of insulating foam needed for cold-weather use. For a tall person the size works out as 490 mm x 670 mm, which weighs an appreciable 340 grams. We can supply a channel mat (minus permaflate) at about $US 22 plus postage.

This is the distinctive moulded back skin on the channel mat.

Any mat is inserted into the permaflate as shown below, The pillow (or buttock pad) is flipped back, and the mat slid in underneath the top section. It is pulled through until it extends under the buttock pad by about three inches minimum, and the pillow by about one inch minimum. This overlapping coverage stops real cold from getting through any gaps between the mat and the pillow and buttock pads, all of which are good insulators. If you are shorter, with less distance between the two pads, extra overlap does no harm, but you are more likely to want to shorten the mat to save weight and bulk. Inserting the mat is not a difficult business. During an airbed-testing night, the temperature dropped unexpectedly to freezing point in the early hours of the morning. Half-asleep and stupid I pushed in the insulating mat. In five minutes I was once more warm as toast, and knew no more until morning.

Short airbed sleeping

A short mattress wins in lightness, ease of assembly inside the tent, and the space occupied on the tent floor, but you have to put your lower legs and feet somewhere. Snow camping is not the only variety that matters, but it does emphasize that anything in contact with the floor of the tent is going to get very cold indeed, and the same is still true at most times of year. Fortunately most hikers carry a large rectangle of insulating material with them. It's called a backpack. The buttock pad on the top of the permaflate has at least four functions. One of them is to raise the upper legs and knees so the lower legs bridge across to the feet which rest on the backpack. I was surprised to find, with buttocks resting against the pad, that this is comfortable both lying on my side, with knees bent, and lying on my back. In each case my head found the pillow. If your pack is snow-covered, beat the snow off. If it is soaking wet, wipe it off and put it in a thin polythene bag, which will add five grams to your load.

On a flat tent floor, much of the skidding and slipping a camping mattress performs underneath you when you turn over is due to the remarkably low weight of modern examples. The clothes-packed compartments significantly raise the weight of the permaflate and it feels much more stable underneath than the straight airbed. You can stripe the base of the airbed with Silastic silicone rubber to raise the 'stiction' to the groundsheet, but I have not done this. The backpack footrest seems not to wander much. If the tent floor slopes, the permaflate slips with the best of them, but once the tent is pitched with my feet down the fall line, and the harness points are connected to the pegged-down loops on my tent the permaflate is firmly anchored. I would in this situation start to slip off the end of a normal camping mattress, but another function of the buttock pad is to stop you slipping down the bed, and it works.

Below is a top view of a permaflate mounted inside a two man ridge tent that has been fitted with support loops.

An enlarged side view shows the top of the permaflate secured to one of the extra tent pegs.

The four sewn points are critical. Each has a loop made of nylon braid or similar sewn on both the inside and outside of the tent groundsheet at a carefully measured location. The loops outside the tent are pegged to the ground with four extra pegs, leaving four free loops inside the tent to which the permaflate can be secured. Note that when the permaflate is strung or strapped between these points, all the stress falls on the four extra pegs, and there is no additional stress on the groundsheet at the sewn points. The groundsheet remains watertight. In practice, the change in feel of the secured mattress is remarkable. It just stops walking around. Also in practice, the sewing of the two-loop joints into the tent is a long and painful business. More detailed instructions on technique will be provided if required, but unless you are reasonably competent at hand or machine sewing, you may have to do without a harness system.

Practical on-snow testing

I took up to the snow, bundled inside the Sliding Barrel sledge (see Colour Supplement) enough gear for three days, including the short permaflate, a channel mat of the right size, and a piece of high grade half inch commercial EVA closed-cell foam. The snow under the tent was stamped down to compact it, but remained dry and was probably at about minus two Celsius.

I first sat on the commercial foam and the top mat for about half an hour on each, with a sleeping bag wrapped round the top of me to keep warm. There were no significant differences beween the two as regards posterior warmth, but memory said both were much warmer than sitting on a six millimetre mat on the snow. I then stacked the two thick mats, making one inch of closed cell foam, and sat on that. The result was very slightly warmer than one mat. The conclusion is that at half an inch of insulation on moderately cold snow, you have most of the benefits of increased thickness.

I spent a leisurely breakfast sitting on the permaflate with the channel mat fitted, underneath a large sleeping bag. Afterwards as expected, the top of the mat was very warm indeed to the touch. What was not expected was that the underside of the mat was not as warm, but still plainly warm to the touch. Beneath the mat was the airbed, the groundsheet and the snow. If the commonly-held perception of the insulation value of airbeds were true for the inflated section of the permaflate, the underside of the mat should have been stone cold. As well as providing comfort, the airbed section improves on the already good insulation.

Finally, sleeping was no problem, although hauling a sledge up the mountain the preceding evening may have had something to do with it. A new sensation with this thick mat was that of sleeping on something that was actively warm. This is a pleasant feeling indeed. When sleeping on my side my knees go over the edge of the airbed, and there is enough height above the ground to stop the sleeping bag touching the floor. The sleeping bag round my knees was noticeably cooler inside than the rest of the bag in contact with the mat. The pack, with a couple of inches of new snow dusted off it, supported my feet all night and kept them warm.