Just received. The mat is double-sided (gray on one side, white on the other), with measurement lines on both sides. Rotary cutter worked great on thin suede pieces. No marks on the cutting mat. I hope I can change the blade with a titanium one later. I think that pressing down too hard with the cutter may accelerate damage to the mat, so I'll only use a sharp blade. The ruler is great. Measuring and cutting the fabric was the most tedious part of my sewing projects, but this cutting set removes the tedium! Thanks to Fiskars. A sturdy, well-thought out cutting set.
Update September 2, 2017: Just used the set to cut very thick leather with layers of suede backing (from an old leather purse I'm recycling). I had to run the blade over the material several times, but no problems.
Update January 21, 2018: Used the set to separate the pages of a thick book, so that I can comb-bind the book. Worked perfectly! I thought I might damage the blade because the book is so thick, and I had to cut through the spine, but no problems! The mat was indispensable.