I have 3 different sizes of the Olfa mats, 24 x 36,18 x24 and two of the 12 x 18. I've had them for years and not had any problems with them. The 18 x24 Fiskars mat warped after about a year, never exposed to heat either.
I never use the lines on the mats as they aren't accurate with the Omnigrid rulers I use, there is about 1/8" difference.
Sharon in Texas
Last edited by purplefiend; 05-09-2014 at 08:28 AM.