Disposable Underpads come in many different sizes and thicknesses. There are some that are tuckable, so that they won't slide on the bed. There's some that have stickies underneath to resist movement during the night. There really are a lot of different kinds of disposable underpads, and some of the differences are simply to keep them in place, while others have to do with absorbancy. Thicker pads are usually more absorbant, but not always. A good quality pad can be absorbant and still be thinner than a lesser quality pad.