Mesh lingerie bags are widely sold to protect lingerie and other delicate fabrics from damage in the washing machine. They are also known as wash bags. An example of such a product here.
Protects delicate bras, panties, slips, hosiery and sleep-wear from snags, tangles and tears
I've been using them with my lingerie for the last two years or so, and I haven't noticed any protective value in using the bags. My lingerie seems to get damaged at the same rate as before using the bags and sometimes bras snag on the bag itself. I was wondering if there is any evidence at all that they do what they are advertised to do, or are just a gimmick device.