Parafilm is the gold standard for providing a breathable seal for Agar Petri Dishes. It's the first choice for labs around the world for sealing petri dishes, test tubes, and all types of containers. We highly recommend using parafilm over grafting tape, micropore tape or anything else for that matter.
To apply the parafil to a petri dish, remove the paper and hold the plate in your left hand. Then use your thumb to hold one end of the Parafilm strip. Now with your right hand carefully stretch the Parafilm around the dish. Work your way around the plate stretching only 1 inch at a time. Be careful not to stretch it too far or it'll break. The strip should wrap 1 and 1/3 times around the plate.
Parafilm is great for sealing plates but please keep in mind that it's sensitive to heat. Keep your sealed plates in a room or container where temps don't go above 80 degrees. Otherwise the Parafilm begins to break down and split.