Foil has been accepted everywhere I have been (make sure it is a bag rather than blanket you purchase, the latter is sometimes refused by Mountain rescue teams if they do a kit check). I don't carry the orange jobs anymore as they are too bulky.
Lifesystems I think is mine, take it out of it's original bag, put it in a airtight gripper bag and squash it down as flat as poss. then seal the airtight bag