Wire mesh?

What is the "wire mesh" that goes behind the key slots? And where can I get it??

I use window screen.

Ah clever, thanks for the tip

I get my wire mesh from micheal's. I'm sure you can pick it up from any arts and crafts store. I typically use the larger gauge as it fits the look better IMO. Also, in silver. I've seen others use a black plastic, but I feel the metal looks better...