They used a regular bed sheet held between themselves and an IR camera to show that the sheet was sufficient to block the IR signature, effectively "hiding" them from an IR motion detector alarm.
I would think the space blanket would work IF it did not come in contact with your skin. That would be the trick, to make sure you don't touch it.
I'd be willing to bet a decent layer of wool and a space blanket wound do the trick.
Hopefully you don't need to be quite while performing this trick because I haven't seen a space blanket yet that didn't make a ton of noise.