Does anyone have recommendations for window screen mesh to keep out tiny gnats?

Sorry, I can't think of any screen I've ever seen that has holes small enough to keep out those real tiny gnats.

Then if you find it, with screen that finely meshed, it will reduce air flow if you are using it to screen in a porch or deck.

I like the above poster who sprays his screens with pesticides to try to control them.

The finest mesh screen I've ever seen were some of the real old ones on my house when I bought it since they were made of extremely fine mesh copper or brass. That and the fact they were so filthy from having dirt cling to them made them almost not even look like screens.