Mat board made of cotton – “rag” board – is multiple layers, or plies, of cotton board that have been color dyed and combined in 4-ply, or 8-ply versions.
The best picture frame mats you can buy? 8-ply rag matboard.
8-ply rag is museum-quality, long-term conservation matting. It’s inert, which means it won’t change shape over time. It’s also acid-free. 8-ply is exceptionally thick, so its bevel is a deep ¼ inch, adding considerable depth to the picture framing package it’s in.
The downside of cotton rag custom mats for frames? They come in fewer colors because they’re made with dyes less likely to have harmful components.
