I was just wondering if you could zip it up like a sleeping bag as well as having it open... Might be a bit more versatile for kids' camping... I was thinking it might make a good project for t'lad during the summer holidays (last year he made a pair of jeans - his first garment project! Aims high, my kid!). As a scout, camping and bivvying are part of the game, and he might think it fun to make more of his own kit. It can be a lot cheaper than buying if you don't factor a time price in, too!
He also runs hot, and last year at Kandersteg he spent most of the camp on top of the open bag, with just a corner flung over if it got cool at night. Thanks for clarifying the clammy point. I shall need to look into fabrics in more detail, I can see. Bog standard parachute weight shower proof ripstop in mad colours I can get easily, especially if I can use odd shaped bits left over from making 'chutes, kites, and hot air balloons! <img src="/forums/images/graemlins/laugh.gif" alt="" />
Certainly a project to think about, as it would be a light thing to carry for over-night hikes and 3 day expeditions.