It depends on a variety of factors, including ambient air and surface temperatures around the blanket that will determine its blending in capability, (lack of) effectiveness of covering body parts for long durations and difficulty in defeating stand off range of sytems equipped with FLIR which can usually detect targets before the targets even know they are being observed.
Short answer- do-able with alot of constraints. You might get lucky. You probably won't.
Thanks. The question wasn’t just about intentionally hiding, although I was interested in that, but also about situations where you might want to be found. Like being lost in the woods. You’d like searchers to find you while also trying to avoid hypothermia.