Why Technical Running Apparel?
Warren Greene of Runner's World addresses the question in this article:
Technical apparel may seem extravagant, but as your friends have already found, once you go technical, you don't go back. Technical apparel is made from fabrics that offer performance features and benefits that your old cotton T-shirt doesn't.
Technical apparel that's worn next to your skin—whether it's a top, sports bra, tights, or underwear—is designed to pull, or wick, moisture (that is, sweat) away from your body. Clothing made of cotton, by contrast, holds sweat, which can actually make you cold and miserable, even on a warm day. Technical clothing also dries quickly, a boon no matter the temperature. For beginning runners on a run/walk program, gear made of high-tech fabrics can be particularly useful as it moves sweat off you during run portions so that you're warm during the walk sections.
Technical clothing is comfortable for another reason: Many items are made of lightweight, stretchy fabrics, making them less bulky. On cold days, instead of piling on hefty layers, a layer or two of thin (but insulating) pieces of technical wear will keep you toasty without looking like the Michelin Man.
Another advantage of technical running clothing is that it's designed for athletes. Just about every runner I know has a story about the "wow" they felt the first time they ran in a technical top. Often they don't realize how uncomfortable their other clothes are until they make the switch. This is especially true for women who try technical sports bras, which are made with flat seams to reduce chafing.
This kind of attention to detail increases the cost, but because most technical garments are well-made, they last a long time and you'll get your money's worth from them. This is a great time of year to buy winter technical apparel on sale, as specialty-running retailers are making room for spring and summer clothing.
A long-sleeve technical top is a great piece to start with. Get one and give it your own wear-test. Chances are your old running wardrobe won't see much action anymore.