Wool, cotton and fleece: good for diaper covers? Im worried about offging from PUL's.?

My instinct would be to go with cotton. I wouldn't go with wool, simply because it's not guaranteed to be hypoallergenic (I, personally, am allergic to wool) and would be really hot in the summer. I don't know much about the hemp or bamboo versions, but I wouldn't think the absorbency would be all that different from cotton, and I'm sure they'd be more expensive.