I keep a couple of the thin fleece blankets and poncho liners around, according to the US Army the liners are as warm as a wool blanket. The liners are a lot lighter and dry out quicker than wool too.
I've actually got a liner at home, and I doubt they are. Maybe for a comparable size? All I know used to use them at the ambulance station, and it got mighty chilly. I have seen the Thinsulate ones in Brigade QM; perhaps those would be an optin?