Swimsuits are a delicate balance of form, function, and fabric. The fabric stretches with the body, but it can also shrink over time in the water. This means that swimsuits will change shape and size when worn in different temperatures of water.
The answer to this question is not as easy as you might think. The answer depends on the type of swimsuit you are wearing.
A swimsuit that is made of stretchy fabric, such as Lycra, will stretch out in the water and can become looser. A swimsuit with a thicker fabric, such as nylon or polyester, will get tighter in the water because it will shrink when wet.