The modern bra is a huge advancement over those brassieres worn by our ancestors, but they are still delicate pieces of clothing. Most bras come with specific instruction on how they should be laundered. Sometimes you have to visit the website of the brand to find them. If you cannot locate the instructions, there are basic guidelines to follow that will help make your bras last.
Hand Washing
A little elbow grease goes a long way with bras. They are delicate items, so putting them into washers and dryers is like putting a Faberge Egg in the dishwasher. It is going to take a beating. Your bra will be pulled and stretched as it gets caught up in other clothes. Pulling and stretching are very bad for bras. Pile all your bras up for a week and wash them by hand in a sink then let them air dry. Do this and your bras will last at least twice as long compared to using the washer and dryer approach.
Detergent
Bras are often referred to as the "delicates" for a reason. We are not scrubbing the grout in the shower here. Cleaning a bra should not be an occasion to do some venting. Relax and use a detergent that is very mild. This will keep the cups and stitching from becoming frayed and worn.
Temperature
Like your water warm? Well, I have some bad news. Bras should be washed in cold water. Cold water is the only temperature that will not tighten up the material in your bras. This means it will fit the same every time. If you use hot water, the cups will tend to shrink up a bit. This will require a bit of stretching when you first wear the bra again. Stretching and contracting is bad for bras, so it should be avoided. Suck it up and wash those bras in cold water.
So, how long will this extend the life of your bras? It depends on many factors, but you should see double the life compared to washing them in the washer/dryer approach.