There are 2 distinct fabics used within swimwear. These are chlorine resistant and lycra.
Lycra has wonderful stretch properties and is used for all the lovely prints and colours, it fits like a glove but it doesn't like chlorine! If you swim more than once a week a chlorine resistant suit will be the best investment particularly if it is going to be left wet in your swimming bag all day at work, but the polyester/pbt fabric has two drawbacks - it doesn't stretch very much and the colours are dull. If you decide to buy a chlorine resistant suit you would be best advised to phone the shop and arrange to have at least 2 sizes sent for you to try on as it must be a comfortable fit - if it is too small it will cut on the shoulders when you are swimming, too big and it will move on you and leave marks on your neck and make you sore.
If you decide to buy lycra then there are one or two things you can do to prolong the life of your suit. Buy your suit in a size that fits snugly as it will stretch over time. If you shower in it after your swim then give it a good rinse in cold water afterwards, drop it into your swimming bag and once home give it another cold rinse and hang over the bath taps to dry. Never wrap it in your towel - if there is any chlorine left in the suit you will heat it and the chemicals will destroy the lycra even quicker. Never machine wash your suit, lycra doesn't like hot water, soap powder or fabric conditioner, and NEVER PUT LYCRA IN A TUMBLE DRIER, you will destroy it.
If swimming regularly or at a club standard, a swimming bag is a great investment. Designed specifically for the function of going to swim, they have a mesh compartment for your wet costumes and trunks to keep seperately from the rest. With spacious amounts of room for all your clothes and belongings.