I can't say enough about a poncho liner,,had to get used to using them in Nam,,during the monsoons,,sleeping on the ground ,,with a poncho liner only,,even wet,,they do give off heat..40-50 degrees and pounding rain,,they work,,double them up,,and squeese under them,,your warm..even wet. I own 3 of them,,and nam one is still kicking with holes starting in it,,its finally about wore out..and newer US issues are even heavier than those we previously used and better!