I agree with what Swissgreys says.
The 2 layers of fleece means the two outer layers. So if you want to make yourself a ready made liner (to avoid having to layer things yourself), then you would have two layers of fleece, and inbetween those two layers you would have an absorbant layer, like towels. Sew all that together and voila, a ready made liner. The bottom layer of fleece is not really necessary, although it does help to keep the moisture inside, by the absorbant layer, rather than having it seep straight through onto your correx, but the other nice thing about the bottom layer of fleece is it means you can use either side of the liner as the up side. So like my one liner is purple fleece on the one side and blue fleece on the other side, that means this week I can have a purple liner in my cage, and in two weeks (becuase I would have to wash it after 1 week so would use a different one then) I can have a blue liner in my cage. One liner, two choices.
If you're just layering, however, then you only need one layer of fleece, put on top of an absorbent layer like towels.
