If your steam iron isn’t working as well as it should, it could be due to the residue from synthetic fabric clogging the steam holes. You can fix this by pouring 1 cup of white vinegar in the water tank. Set the iron upright and run on the steam setting for 5 minutes. Pour out any remaining liquid, then fill with water and run on steam for another 5 minutes, pour out, and then refill with water as usual. The vinegar will have broken down any built-up gunk.