i have a couple of mats in different sizes and when i went to buy a new rotary cutter, for only a dollar more i could have another mat that was 18" x 18". really weird promotion. but i had a coupon, so what the heck!
my dh cut the mat 18" round and attached it to a lazy susan from home depot. when i'm in my grave, that thing will still be rollin' around. since i tend to use the smallest mat for each use, i really love the rolling one. it's perfect for 12" squares. it's a fiskars, like the cutter.