I have been using these zippered plastic and mesh cages to wash my bras for several years now. Bras are expensive and difficult to wash. Most women hand wash them, but these little cages protect my bras and keep underwire bras from being misshapen. I hook the fastens on my bra together to keep the hooks from catching on things, put two bras in the wash bag throw them in the washing machine on the delicate cycle, and they come out fresh and clean and ready to hang dry. These little gadgets have doubled the life of my bras.
I buy mine from our local Daiso store, but I’ve found them online on Amazon and other places. The important thing is that they have a round plastic frame in the top and bottom to protect the bra. Most of them also have a little piece of elastic that you tuck the zipper head into to keep them from snagging on other stuff in the wash.