I tried freezerbag cooking, made my own insulator out of reflexite, etc. The main problems for me where the plastic smell and the awkwardness of eating out of a floppy bag. Didn't taste any different so those are just minor annoyances. Still, I swithced to a wide mouthed plastic thermos. Same concept obviously, just pour and let sit. Yeah it weighs more than a freezer bag + cozy but the pluses are that its way easier to eat out of (its got a handle) and it insulates far better than a cozy. Plus its got a handle. Then again when backpacking I've never been an ultralighter so YMMV.