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Is a t-shirt or a sweatshirt better?
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A t-shirt is usually made of cotton, and a sweatshirt is usually made of polyester. Cotton absorbs moisture more quickly than polyester does, so it's best to wear a t-shirt when you're going to be doing activities like running, biking, or swimming. Sweatshirts are generally warmer than t-shirts, so they're good for cooler days.