Everyone has had a pair of sunglasses that over time warped so they didn't rest comfortably anymore. To bend them back in to shape, all you need is a little hot water to soften up the plastic a bit — just be careful to bend them, not break them.Photo by Brian Gurrola.
The hot water softens the plastic up enough that you can twist your glasses back into shape, especially if they've only warped from wear. This won't work if they're cracked, and you don't want to risk this with prescription glasses where the lens may be damaged by the hot water bath, but if you love a pair of sunglasses and they don't sit right anymore, this can help bend them back into shape.
Real Simple also notes that if your glasses are a bit more delicate, or you want a tip you can use with prescription lenses, try using a hair dryer to spot-heat the part of your glasses you want to bend.
Easy Sunglasses Repair [Real Simple]