Nylon wind pants, or "swishies" as they are commonly called, are comfortable and versatile enough to wear for a variety of activities. However, when they rip, it may seem like the only thing you can do is throw them away. This is not true—although simply sewing up the tear will not work (the nylon will only rip more), there is a way to successfully repair ripped nylon pants.
Most likely, your nylon wind pants were ripped from a fall or at least while you were wearing them. So, chances are, the pants will be dirty. You should not repair the pants while dirty, as dirt will get caught in the fibers of the fabric. You should also not wash the dirty pants in a washing machine, as this will cause further fraying. Wet a wash cloth and pour some mild hand soap or baby shampoo on the ripped area. Lightly scrub until clean, and then let the pants air dry before you start to fix them.
Buy some urethane tape, such as K Tape (see resources section). Trim any frayed fabric along the edges of the rip and turn the pants inside out and place the ripped section on the table Gently pull the rip closed as much as possible as you place a piece of the tape on the ripped area, making sure to completely cover the entire rip. If the tear in the pants is a big one, you may have to use several pieces of tape and line them up.
To make sure the tape stays in place, sew a zig-zag stitch around the edge of the patched area. This way, if the adhesive ever fails, the patch will still stay on. There are likely to be some frayed edges where the rip occurred on the outside of the pants. To keep the fabric from fraying any further (and to add another layer of adhesive), coat the outside of the rip with clear nail polish. This will bind the fibers of the fabric together and stop fraying in its tracks. If you find that the edges of the patched area are rough against your skin cover the patched area on the inside of the pants with a piece of soft fabric, such as fleece, and sew it in place.