The Thermarests are good if expensive, self-inflating mats. They do tend to be a bit bilky though. Thermarest also do something called a Z rest and that used to fold up very well. They were called Ridgerests but there is also a folding version. I'm sure that they used to make two thicknesses as well because I used one of the heavy duty ones when I did a bit of mountaineering LINKY
Thermarest also have these now. Never seen them before - looks like the bloke in picture is about to blow a goose CLICKY
If you're really looking to travel light, I've had a survival mat for years. Its 3/4 length but only 2 or 3mm thick foam with a metallised reflective side. It folds up to almost nothing.
I can't remember where I got mine, and unfortunately, the only place I can find them on tinternet is a caravanners site.
Beware when "cutting down for size" a standard issue mat. I mangaged to trim mine right down, almost exact body width and length ways from top of shoulders to just below my arrse. Imagine how I chuffed I was about being able to fit my roll mat inside my bergen.
It never occurred to me that my calves would still be in contact with the (very) cold Dartmoor ground. One of the coldest and longest nights under the stars ever....
There is nowt wrong with having a roll mat bungeed onto the front of your bergan...!
To be fair lads, the issue roll mat isn't that bad. I picked up a thermarest which, when conditions allow, is an awesome bit of kit. But for wet, windy, messy and busy conditions, you can't go too far wrong with the issue roll mat...
I know the dutch or germans do the folding up one, but these are very thin and don't do a lot for you.