Yes, it sounds crazy, but hear us out: The next time you buy a new pair (and before you wear them), run them under water until they’re damp. Then place them in a plastic bag and freeze overnight. Take them out and give them a day to defrost and thaw out.
You only need to do this once--after that, you’re good to go. The chilly temps firm and strengthen the individual fibers of your tights, making them less susceptible to runs later on!
Original Post Diego Zuko