Mountain Hardwear gets their proprietary synthetic insulation on with the UltraLamina 32. This +32F bag actually uses two of MH’s flagship technologies: Thermic Micro insulation and welded Lamina construction, resulting in a 2lb weight and small compressed size.
Thermic Micro is a short staple synthetic that is a step forward in loft and compressibility; still not down, but getting closer – and, oh yeah, you won’t DIE if it gets wet. Bonus. The Lamina welding adds warmth, saves weight and, if done right, doesn’t compromise durability. This bag hits all the high notes and adds a few more: dual half-zippers save a bit of weight and let you sit up comfortably, and the zippered pouch next to your head will let you keep whatever nasty little "sleep aids" you use handy.
The temp rating is a bit optimistic unless you’re a warm sleeper, but this is true of just about every manufacturer. If you’re out in borderline freezing temps you’ll have a mid-weight insulation layer with you anyway and combined with this bag you’ll save some weight. If you like to sleep commando-style, and/or if you’re just a cold sleeper you’ll want to bump up to the UltraLamina 15. It comes with a three-strap compression sack, but it ripped the first time I put some ass into it so plan on getting someting a little more bomber there.