I've really liked the non-stick silicone backing mats that I have. I use them all the time. They fit perfectly in our 12x16" jelly roll pans. My cookie sheets are a bit bigger though at 14x16". I could fit more on the sheets if I could find silicone mats that are two inches wider.
Are there silicone mats that are sized to fix 14x16" cookie sheets?
Don't know if you got it yet, but I just purchased one from Kohl's. It's a Food Network branded product. I had hoped for two, but store only had one. There's some issue with the SKU from the bar code on the product, but they do carry the product. Here's the link. http://www.kohls.com/product/prd-756153/food-network-14-x-16-baking-mat.jsp Here's the SKU that they had to look up in the store to ring it up: 91482863. You can look up if your local store has any in stock, but not the quantity.
Wish I had it yesterday before I baked three hundred cookies. I'll be ready next year. Tired of cutting parchment and it sliding around, especially with balled dough cookies!
I have been looking for the same size as a gift for someone. 14x16 is actually the standard size for what is called a "cookie sheet" - the more square size pan with a lip on only two sides. I did just find a baking mat in this size listed on the Kohls website, but I've yet to actually see it.
I use half sheets at my house and find this size to be very versatile and easy to find Silpats, etc. for. Plus they are inexpensive and easy to replace as needed.
The standard sizes for sheet pans in the industry (at least for the US) are based on the "sheet pan", and are approximately as follows, at the edge of the rim:
Your cookie sheet is not one of these standard sizes, so you are unlikely to find a common silicone mat (or pre-cut parchment supply) sized for it. Of course, you can always use the next smaller size....
In fact, you are unlikely to find silicone mats for sizes other than these, and cutting them is definitely not recommended. Mats sized for standard sheet pans will be just a bit smaller.
I do not note any odd sizes on Amazon, but that doesn't mean specialty sizes don't exist. They would be a niche item, however.
On the other hand, sheet pans are very inexpensive, and incredibly versatile. One of their myriad uses is as a jelly roll pan. You could certainly buy half sheet sized mats and pans, and use them together, for jelly rolls, cookies, roasts, or almost anything else.
Another alternative is to purchase baking parchment, and cut it to size as required. You may get 2 or even 3 uses from each sheet if you are careful.
