I would suggest Ying, that she is soaking the sides cause the wee can get through the sides, as the rest of the nappy is too dense for the wee to penetrate at the rate that it is entering the nappy.
Just a suggestion, maybe try the two nappy system and do some layering - like fleece liner, some microfibre, then some cotton, then the hemp and bamboo. That way, the thirstier fabrics suck the wee in quickly as Becky does it, then the other fabrics will hold it.
Geez, I must have done some night nappy playing to get all these ideas
