Step 2: Melting and forming
If this is your second retainer you are making, make sure you have the previous one in your mouth. This way they will fit together when you bite down.
Fill up the glass cup with water and put it in the microwave until it bubbles (around 2 min). Pour the shapelock plastic into the water and let it sit until it is all clear. Use a fork or something else to press the plastic together into a ball. Once it is totally clear, take it out with a fork and pull a chunk off of it, around 5 g. Then shape it into a half ring in the shape of your teeth. Make sure it is wide so you can fold it over the teeth. (See pic)
Do not try to press it onto your teeth yet. Once it is in a basic half ring shape, put it back into the water to let it soften again, then take it out and fold the edges in. (See pic)