Honesty is not supposed to be an advantage in Marketing, but the straight answer is, we have to. It is an integral part of the design. One of the many functions of the buttock pad is to spread the heavy load of the upper legs across the whole lower end of the short permaflate, rather than crushing tube ends and accelerating tube wear. The buttock pad also equalises pressure across the six tubes. Note your hips do not actually rest on top on the pad, which feels most unstable, but just before it, so your buttocks contact the pad. If the pillow to buttock pad length is tailored for you, you sit on the inflated permaflate, normally in your sleeping bag, as far down as you can slide, and when you lie down on your back, or on your side with knees bent, your head contacts the pillow. This position is much more stable than on a flat mattress of any description, and you, or at least I, tend to stay in this position while asleep. Such normal camping adventures as slipping down the bed, or having whatever you are using for a pillow escape, do not occur on a tailored permaflate.
The 1200 millimetre permaflate as pictured is used by a fairly tall camper, and the pads on top are separated by the maximum distance possible for this length of airbed tube. If you are a camping basketball star, you will need a longer airbed. To fit shorter campers, the buttock pad remains where it is on the pictured airbed, but the pillow pad is sewn in a lower position. This puts spare airbed length above your head rather than under your legs, but trust us, extra airbed length farther down than the buttock pad is a positive nuisance. The pillow pad can be sewn on to the rest of the airbed with a single line of stitching, although you must take the tubes out first! The sewing edge can be pinned down or stuck down with double-sided adhesive tape, and the single straight line of stitch put down with any normal plain sewing machine, or hand sewn, since one 18 inch long line of stitch will not take you all night. Any pins left in the work afterwards will puncture the tubes.
Since the tailoring is easy alterable by unpicking this stitch line, we normally ask you for your vital measurement, and stitch on the pillow pad for you. It should fit, but if it does not, you only need to correct this one stitch line.
The vital measurement is from the top of the shoulder to the ball and socket joint of the hip. Lift your knee to find the hip joint. I measured my own at 23 inches, but my wife measured the same apparent distance at 22 inches. The corresponding distance on the pictured permaflate between pillow and buttock stitch lines is 21 inches, so the tailoring rule is to subtract one and a half inches from the vital measurement and put the stitch lines this distance apart. Precision to one inch is ample, and you can make adjustments by varying the amount of clothes packing in the pads.
We hesitate to add, but will do so anyway, that the impact, wear resistance and comfort of the design all centre round the buttock pad. The pillow is just there conveniently in the right place. You can use the permaflate without tailoring, by packing the buttock pad and replacing the pillow with the normal pile of camping clothes used to support your head. The problem lies in persuading airbed users that what looks for all the world like a perfectly normal pillow actually goes at the opposite end of the airbed! If only one pad is used with this design, and that pad is at the head end, the result is short-lived and uncomfortable, although not actively dangerous to health.
The comedian walked off stage. A fan asked "did you kill them?", "No", he said, "They were dead when I got there."
The writer, over the years, has bought a great many airbeds, of which only one, an early nylon/PVC laminate type from Taiwan, actually remained inflated after one night. Most were flat or flattening by the early hours of the morning. In a great deal of camping the writer has never punctured an airbed of any variety, and has never bought one with a classic point puncture. Where did all the air go?
It is possible on a warm afternoon to struggle with an inflated airbed in a large bath half-filled with water, and find out from where the air is leaking. So far the answer has almost always been seams at the edge of welds, or imperfections in the welds themselves. These leaks of course cannot be patched. After much hard camping, the exceptional nylon/PVC airbed began to slowly leak. Porosity was developing along the length of seams as they slowly pulled away from the welds. Since new this remarkably good airbed had blown out stoppers at the slightest hint of overinflation, but as airbeds go, it had performed very well, It was sadly scrapped.
Another category of airbed is the tube and sleeve type, of which the permaflate is an unusual twin-tube example. A British Army surplus type had welded clear PVC tubes, almost all of which had seam faults. A high technology USA-made lightweight was made with tubes that had no side seam. The tubes themselves lost no detectable air, but the valves were neat devices that you blew through then pulled with the teeth to seal. Half the valves leaked. One night the weld at the end of one tube simply blew apart, and another airbed was junked.
It became obvious that to produce a non-leaking airbed it had to be a tube and sleeve type, with the absolute minimum of welding to fail. Polythene layflat tubing was cheap, had no side seam, was non toxic and easy to weld, so it was selected for the tubes. All forms of valve or stopper currently in use had serious problems, so a step was taken backwards to a rubber bung in a hole. The permaflate was born.
Both on the long domestic 'testbed' and camping out in the field, no punctures occurred, and any problems were fold, kink or weld related, and they all occurred at the foot end of the airbed. The rest seems to last for at least one year of use every night. As each problem has turned up, the design has been modified to fix it. An addition has been made to the 'testbed' of a small sheet of closed cell foam above and below the foot end of the bed, and this seems to have stopped the heavy foot pounding that was shortening the life of tubes. Much of this is due to the tester being longer than the bed.
Each tube is leak-tested betore despatch. The tube is inflated with an air blower for speed and cleanliness and stoppered. One end at a time is put in water while the tube is squeezed as hard as possible to raise the internal pressure. Bubbles of course indicate a leak.
The main length of the tube has no welds and is most unlikely to leak. The length is visually checked for flaws.
It is possible to put a little air in a tube and roll up both ends until there is a short length of pressurised tubing between the hands, which can be immersed in water. If you roll one end, and unroll the other, you can work along the length of a tube. In practice it is much easier to blow up the whole tube, look for a flaw, then put the end of your tongue on the flaw while squeezing the tube hard. Any bubbles emerging can be easily felt. Most airbeds lose air so fast that temperature effects are not noticed. The permaflate retains air for about three weeks, although there is a slight initial loss of oxygen by diffusion. If the evening is cold, within ten minutes the tubes will be much softer than when you inflated them. There is still normally plenty of air without reflation. What not to do is to blow up six tubes, then reflate the first tube you blew up because it is noticeably softer than the others. Of course it is since it has cooled down.
One horrible night you are going to find a flat tube. If you are too sleepy to care, put any odd clothing in a line on top of the airbed to fill up the groove that should not be there. This is surprisingly comfortable, and two grooves per airbed can be filled before the system gets out of hand. The centre sewn division, where all the weight goes, really needs two inflated tubes.
For peace of mind with punctures, it makes sense to follow the car example, and carry one spare tube, and an extra stopper or two. I have not yet punctured a permaflate tube, and if punctures occur as often as to my car tyres, I shall need the spare tube in about 15 years time.
Before starting, a book recommendation for a series of slim volumes on camping written by Cliff Jacobson and published by ICS Books Inc in the USA. They will be referred to in the text as simply 'the Book' since they are that good. Winter camping is of course covered.
Airbeds are well-known as three season devices that are left behind when the snow falls. At minus 20 C the gentle cold reaching up from underneath starts to turn into a hungry monster. To go into a little more detail without stating the obvious, a sleeping bag expands a great deal when unpacked, and since thickness is the way insulation works, over the top of you where there is no pressure it keeps you warm. If you were tough enough to lie straight on the ground and sleep, the body points in contact compress the sleeping bag material beneath them, and cut the bag insulation dramatically. The result is a series of icy points on the contact areas. A closed-cell mat insulates better than an airbed, but you will notice when you try it you are still virtually sleeping on the ground as far as comfort is concerned. The closed cells do not compress overnight, so there is some good insulation, but underneath you the sleeping bag is still heavily compressed at the contact points, so the insulation is not as good as it might be. If you sleep on an airbed, some heat is lost since it is a poorer insulator, but the spreading of the body weight that makes it so comfortable also allows the sleeping bag to regain some of its thickness underneath you. An airbed is a little colder than a mat, but not a great deal.
To keep warm in winter we all have to carry more bedding. The immediate and very sensible response is to carry a closed cell mat and an airbed. The airbed stands on the closed cell mat and things are much warmer. If the airbed fails, you may not sleep, but you will not die. The writer used this configuration for a number of years. The Book says the insulation is better if the mat is put on top of the airbed. One cold night I moved the mat from under the airbed, to on top, after starting to feel the ground reaching up from underneath. It worked. The sleeping bag warmed up and it was back to sleep. A mat on top is much harder to keep neatly in place, but yes, it is warmer. Cheap closed-cell mats tend to compress at pressure points quite quickly, which levels out the bumps at the expense of keeping warm. The worst quality (chinese) mat we can find collapses immediately at the pressure points if you sit on it on the ground, but when used on top of an airbed the load spreading is such that it does not compress at any point, and functions almost as well as more expensive mats.
With a half inch mat insert, the permaflate is adequate for minus 20 C, which is as cold as the Australian Alps will go. The polythene used for the tubes is also specified for flexibility at this temperature. If you are using a permaflate in colder conditions than this, we would love to hear from you.
Assuming you are camped on snow in some shelter, with plenty of ventilation through your tent to sweep the moisture out, a rough guide to minimum temperatures is as follows, assuming you have a one litre or so full plastic water bottle with a plastic screw cap, standing upright in the tent.
The cap freezes to the neck of the bottle, but the water is unfrozen.
Minimum minus 5 C
There is some, but not a lot of ice in the water.
Minimum minus 10 C
With the bottle standing on insulating clothes, and a shirt over it,
some ice is still forming.
Minimum minus 15 C
With the bottle wrapped up in all your spare clothes, a small quantity
of ice forms.
Minimum minus 20 C