Batting is just another name for wadding.
it comes in many types, poly, cotton, mixed, bamboo etc. It also comes in different lofts which is how thick it is. I imagine a low to mid loft would be fine for a sewing machine mat. Any fabric shop that has quilting cotton will have wadding/batting and they'll cut it in half metres, sometimes even quarter metres so you won't need to buy a tonne of it!