Covering Rockwool insulation with plastic?

Hey folks, I'm planning to build some bass traps with Rockwool's "sonorock" insulation. My question is: before covering them with breathable fabric, do I need to put some kind of plastic foil over the rockwool? I'm a little concerned about possibly breathing this stuff in every day. Is it harmful? Also, wouldn't a plastic foil be reflective towards higher frequencies? I hope someone can give me some advice. Cheers, Mika

Many people worry about this. Rockwool is not really toxic, it dissolves in the lung within a couple of weeks. It is just Rock! A thin layer of plastic like Clingfilm will not affect HF. The fabric would absorb it in any case. But may I suggest a modern option available locally to you. These Polyester batts are totally safe and do not even need fabric. https://www.don-audio.com/Caruso-B100-B ... er-Isobond If you are making deep traps, you would use cheap fibre and use a thin layer of Isobond instead of fabric.