Does a thick 4-season sleeping bag negate the need for a sleeping mat?

[Magicdave]

I had to check, it is. It's the Exped Synmat. What a great idea. The insulation lofts as you blow it up, not cheap though.

http://www.ultralightoutdoorgear.co....tra-wide-p4110

[cranmere]

'Way back in the Dark Ages before even foam mats were a Thing, I learned to make a thick layer of dry stuff under my groundsheet to act as insulation and padding. It was fairly effective, but I'll still use my modern Thermarest, thank you.