In reply to martinturner:
Mrs B had a Nemo Fillo under the christmas tree this year (got it cheap in a sale in Melbourne) - limited testing so far, but will be used all next week so will need to report back. Certainly feels less sweaty than the waterproof bladder types tend to, and very comfy when used as a cushion!
Sea to Summit Aeros good (when I can wrestle it out from under my eldest son's head, bah).
At 80g it's a reasonable weight penalty to luxury ratio!
b