1 - Cut the plastic bag with the utility knife using as a template one of your shoes.
2 - Glue both sides of the insole using silicone. Leave a small gap in the upper portion of the insole. Let the silicone dry for 3 hours.
3 - Add the soil through the gap using the funnel.
4 - Cover the gap with silicone once you are done with the soil. The insole should have 70% of its capacity used by the soil. Repeat 1 through 4 to create the other insole.
5 - Place the insole in the shoe.
6 - Stand and walk on it.