Maxi pads are made with 4 layers of bamboo fleece inside. Some have a layer of PUL, which is a totally waterproof barrier. The wool backed pads never have PUL in them. Round pads measure 10.5" x 3" and the Slim pads measure 11" x 3". If you are trouser size 18 or above, go for the Slim Mega pads.