https://www.hobbylobby.com/Crafts-Ho...x-5mm/p/111098
This. It is usually sold in the same aisle as the felt sheets. Cuts with scissors or craft knife. Some of it has a sticky back so you can mount it. Lots of colors.
The advantage of this over felt is bases don't catch on it like felt and it looks more like road. Felt looks better than this for off-road, like grass or sand.