It’s not as weird as you might think playing with a bell cover on your instrument.

Watch this video for information about masking (https://youtu.be/u46GJAnpZ7k)

TCB recommends a cover that is made of 2 layers of 80-denier fabric with a MERV-13 filter in between them.  In practice, this can be made with a particular kind of readily-available spandex, and circular MERV-13 filters can be purchased online.  Many bell covers available online do not include built-in filters, while some do.  When a filter is not included, you can generally “bring your own filter” and incorporate it into your mask.

Where can I get one of these?