I haven't used them in a long time. Usually when I did I'd light the pipe get it tamped down and then put the cap on. If a relight was needed I'd take the cap off, light it, tamp it, then put the cap back on. I'm sure some people just relight through the cap, but I wouldn't be able to speak of if that's harmful or not to the pipe. I will say be careful if you take it off to relight it, cause that cap is metal and depending on how things are it can get pretty warm itself.