for those that might not know UDP is an underquilt protector
They are good for several things. Keeping splash rain off your underquilt,
protecting a big dollar investment from branches/sticks/etc. They also
add another layer of dead air for insulation...and when packing up you can if you want let the whole rig lay on it as you pack up. I try to do the shoulder thing keeping everything off the ground as I stuff it in the sack.
ZQ/TQ make a great one if you are not the DYI type.