These are great. I was worried that the string or bag material would break if I pulled too hard, but they stand up to quite a bit of force, I am able to pull them hard enough to get a good seal on the top and no tea gets out. Haven't broken one yet. The bag allows ample room for expansion. These are superior in every way to the traditional bags like t-sac that have open tops which either allow bits of tea to get into your brew, or if you hang the top over the edge, they drip down the side. Highly recommend these drawstring bags.