There are several methods to build paint ball grenades that include using tubing and cotter pins or ties, however I believe the following is a easy and effective method. First take a paper towel or piece of paper and fold it in half. Put 2 1/2 tablespoons of baking soda into the center and then fold it again creating a square. Use tape to close up sides keeping in the baking soda. Fill a empty water bottle with paintballs and about a cup of hot water. Allow the hot water to dissolve the paintballs. Take paper/paper towel with the baking soda inside and stuff it into the water bottle. Add 1/2 cup of vinegar, cap the bottle and throw your new paintball grenade.