Detach Plastic Straps
If you can, detach the clear elastic pieces from the body of the bra. This will keep them from getting tangled up in the bra unnecessarily during the wash cycle. It also will stop the slide adjuster from moving, which can cause hard-to-adjust slack in the strap.
Use Lingerie Bags
To extend the life of your plastic-strap bras, purchase a mesh lingerie bag and launder your foundations safely. The laundry bag will greatly reduce the amount of accidental hooking that happens during the wash cycle, as well as keeping underwear together and free of garments that can twist and warp bra components. Don't include the plastic straps in the bag; you'll be hand-washing them.
Launder the Bra
Wash your bras in warm or cold water inside of the bag. Hot water isn't good for the synthetic fabrics of most bras, nor their plastic straps, so avoid it. After the wash is done, hang the garment up to air-dry. Avoid tumble-drying the bra, since this will lead to warping of the underwire and wear of the straps.
Cleaning the Straps
Often, the plastic bra straps can become cloudy and greasy with long wear. To cleanse away these body oils, use some shampoo or body wash to wipe off the grime. If desired, scrub the straps with a washcloth or soft toothbrush. Give the straps a fast rinse with cold water and towel dry.