The backer boards are:1) typically 8-6 13 long (2.5M to 3.9M long) 2) and for thickness either: a. Thins are typically 6mm 9mm thick (yielding one wear layer/lamella) or b. Mediums - are typically 10mm 14mm thick (yielding two wear layers/lamellas) or c. Thicks are typically 18mm + (yielding three wear layers/lamellas)3) air dried