We use the Thermarest 3/4 self-inflating matresses as seats in our VOLSKKAYAKs. We fold the mattress double beneath us, single up the back, then allow it to inflate and close the valve before entering the kayak. Once in, the valve is barely cracked open, and you sink until you just contact the bottom of the hull, then close the valve. We find this arrangement very comfortable; it's soft, warm, and the air displaced forward tends to form a soft roll under the back of the thighs. I've often spent four to five hours at a stretch in the kayak with no discomfort, and have never had any problem with my legs or feet falling asleep...