Thanks everyone. Bumbles (including qd) are made of terry cotton, with a fleece liner (see here for a description: http://www.babykind.co.uk/bumble.htm
), they also have an insert, which flaps out in the qd model, made of three layers of cotton terry, so he's currently got that AND the bamboo square. I've found this combination is better than a bumble boosted with two hemp inserts (also from easy peasy), which get soaked through even faster.
Not sure if the two things normally go together, but he also often manages to saturate a 60cm cotton terry (usually a terry tot by Nature Babies or Bright Bots) within 3 hours during the day time.
Might have to dig out the big fleece wrap I've got somewhere, although I wonder if that would all fit inside his sleepsuits(!) Not sure if he managed to leak in a disposable - they were certainly very heavy by morning when we used them on hols. It does all vary a bit, according to how many times he's woken up to feed in the night (more fluid in = more out, unsurprisingly).