Biking is a simple activity that can be done in normal clothes, including cotton of course in a 13 mile ride. In fact, cotton has some advantages over the hyped materials even for riding. They will not smell bad as easily. I find that cotton is generally cooler, especially if it isn't tight-fitting. (Seersucker losse button up for the hot days seems to be the best) More normal clothes are made in cotton, and hopefully you won't go through the hassle of changing every time you go to and from work, so that's a plus. The problem with cotton is that it retains water, but if you are not sweating a lot, that's irrelevant. I've also found that being soaked in cotton in a warm day is no big deal either when going home and I can change. (So, if you are going to change anyway, it's irrelevant). It also took me a while to figure out that if it was hot and I was going to sweat a little, cotton was better than the Champion Double Dry shirts and their ilk. You should be able to use your normal wardrobe for the most part, including a simple jacket and so on.