oven liners....for the bottom of an electric oven. they are great for fmq, and also for ironing
I have several
https://www.amazon.com/s?k=oven+line..._ts-doa-p_4_10
I found these right after I sewed my quilt to a super slider mat (or whatever they were called) when they first came out.
bigger
better
and much less expensive