when you say a liner, are you referring to lining the cash slot, lining card slots to hold cards or the piece you are attaching the card slot to? Each option will change the answer for me
If it's lining the cash slot, I go with cloth. If you are talking about the lining on card slots, ribbon. If you are referring to the backing, 2/3 oz veg tan.
If it's something else, we need to have more details