Hi- I gave up with using foam as a cheap replacement for a bust mat a few weeks ago until i had enough for a neoair trekker. now i enjoy using a bivi for the ease/weight savings, i currently use an rab ascent one which i love(d) until trying out how much space i had within the bivi last night.... its tight to say the least! i had cold spots on my shoulder (as a side sleeper). Im heart broken honestly as i love both bits of equipment but i need a solution for this. I could swap/sell the mat or bivi i suppose. not sure what replacements would be adequate though. does anyone have any thoughts? im sure others have experienced this. im reluctant to put the mat on the outside too as its a bit like an ice rink! again, any insight and advice is appreicated!