The production of Salem cutting mats and rulers began in California back in 1979 as the first American made rotary cutting products. They are still manufactured here in America. They are all produced under the same quality standards as in the beginning. Some selling features are they can be rolled up for travel or storage and are not effected by heat. In fact, with a simple pressing cloth you can iron or press your project. They are soft enough you can pin patterns or small projects down as needed.
The Olfa items are made in Japan and are good products but cannot be exposed to heat or sunlight because of the chemicals used in its production. Excessive heat or sunlight will cause the mat to warp and cannot be flatten back to its original state.

I love, love, love my Salem mat. I bought it at an estate sale and it appeared new. I put it in the trunk of my car...and pretty much forgot about it for YEARS (I was waiting for my current mat to wear out). Finally took it out of the trunk and it had a slight curl. It did, indeed, flatten out. What I love most about it is that you can cut repeatedly and it really seems to self-heal. With my Olfa mat I end up cutting slivers out of the mat if I cut too close to another cut. Secondly, the Olfa mats SMELL when new, and take a while to off-gas. On the plus side, I can get Olfa mats from JoAnn's, which means I can use a coupon.

I don't have any problems with the lines on it that another poster responded about earlier.