Thermarest are a different kettle of fish to an airbed, the clue is in the name, they are designed to provide a thermal layer between you and the ground. They don't have a huge amount of air in (the air inside allows the foam inside to fill out) so wouldn't chill the same as an airbed. Also the material used on the outside of the Thermarest has insulating qualities thus doing away with the need for any extra insulation.
However, if you read the FAQ's on the Thermarest website they advise you to use another thermarest under your mat when camping on snow which is a tad extreme for most of us but shows that even with the best, as Thermarest arguably are, the experts back up what some of us on this forum are saying.
Just put this on another thread as well but Ive got the hi gear air bed that has batteries in it, it inflates in about 4 miniutes with no problems we are still using the same batteries we had last year, you can also turn the air valve round and use the batteries to take the air out as well it goes down really flat and no effort needed for inflating or deflating, it also has an internal pump to put that bit of extra air in if you like it a bit firmer.
> To stop this you should either put a barrier between the ground and the bed (either foam mats, bedding, quilts or even newspaper) or put a barrier between you and your bed (quilt or extra blanket). <
Or prevent the air in the mattress from circulating, thereby transporting the cold from ground to body. And that is exactly what Thermarest and similar selfinflatable do: the foam inside does not as much insulate, but especially prevents the air from circulating. In this way the air becomes an excellent insulator again. Selfinflatables are much warmer due to their insulating properties.
Hi Skatty- you must know what you're talkiing about since you are obviously a regular poster.... but what you're saying there seems quite surprising. Yes there is some logic in putting someting underneath the mattress, but now you're suggesting also putting somthing on top of it! I hope you don't mind me saying it but this all seems like overkill and not really necessary except perhaps in extreme conditions. We've now used our Therm-a-rest Prolite 4 mattresses on several occasions. We used them on their own- no layer underneath, no layer on top (apart from the actual sleeping bag we were using) and we've been as snug as a bug in a rug...
Hi sorry I wasnt really clear I was talking about 'Air beds' and yes it is overkill to have both becasue putting soemthing under the airbed has little or no effect the insulating layer need to be on top of the airbed