Under Quilts 101
An underquilt is used as bottom insulation in lieu of sleeping pad. It consists of sleeping bag insulation that is suspended beneath the hammock where it can insulate the bottom of the hammock without being crushed under the occupantís bodyweight.
ďThe YetiĒ is our torso length underquilt. The idea is that most underquilt users are already carrying a short piece of ccf foam anyway to use as a sit pad, pack frame, fire fanner, emergency go-to-ground bottom insulation ect. As such, it can be used as bottom insulation for the lower legs as well and allow you to cut a good deal of bulk and weight from your underquilt (7-8oz). A short pad under the lower legs doesnít come with the negative characteristics associated with full length pads, such as uncomfortable pad buckeling, difficulty with proper placement, condensation, and packed bulkiness. In fact itís so easy to deal with a pad under your lower legs that you donít even need to put it in the double layer, itís actually easier if you donít. Another benefit of this type of setup is that you can move and stack insulation where itís needed most. For instance, if the temperature unexpectedly drops below the rating of your underquilt, you can stack your torso underquilt and leg pad together for plenty of added warmth if you have to.
A lot of folks also enjoy the added comfort from placing a stuffsac filled with spare clothes/raingear under the knees while sleeping on their back (I do). Aside from the added comfort, this insulates much of the lower legs and allows for an even smaller leg pad for the extreme lower legs and feet if desired. Some more extreme ultralight users even prefer to use their empty (or mostly empty) backpack as their lower leg insulation. Many also find that they donít need bottom insulation at all under the lower legs in warmer weather. There are several options available as fortunately your lower legs donít need nearly as much insulation as your torso does.
As far as adequate warmth goes, you can use any of the bottom insulation options (ccf pad, air pad, or underquilt) to stay warm in just about any conditions, provided you choose an appropriately rated pad or quilt for the temps. Combining them (torso uq and leg pad) gives you the best of both worlds without sacrificeing warmth, and many have now begun using this type of setup year round.