Wow! Surprising comments! I have two opinions: Depends on what you are using it for - For example - I owned a quilt shop, and we rotary cut all of our fabrics - I switched out the mats about every 9 months. My home mat gets changed out every two years or so - I find that when it's newer, my blades last longer (saving me money) and my cutting/piecing is more precise. I also make a point of using both the front and back of my mat - they have the same surface on both sides - and I get very distracted by the lines, sometimes! I use the Olfa green mats, 24x36.... I also don't have a "permanent" sewing space, so my mat goes from flat in the closet to flat on the table quite frequently, so I risk warping it......