In a previous Ask Alison question I answered a similar question regarding silicone baking mats and baking with other silicone bakeware. In that answer I said that I definetely recommend the brand Silpat over any other silicone baking material out there and discussed the various choices and why I believe that Silpat is a superior brand.

Silpat's are made in France and are have been highly regarded in the baking world since the 1960's. The mat is made with interlocking fiberglass that is then surrounded by food-grade silicone. This ensures even heating. As long as the Silpat is stored laying in a flat position it should last thousands of uses and not leach any chemicals into your food. If the Silpat is folded and creases appear I would recommend discontinuing it's use.

Keep in mind that unless you're using glass, pretty much any material that you use to bake is going to have a chance of leaching. Aluminum has been disputed time and again, as has non-stick. Even Parchment paper is impregnated with silicone. I personally own and use a Silpat and feel that it's been proven to be safe and non-leaching.