Whether you should pour by weight or volume depends on your unique molding process. If you pour rubber in smaller quantities, either method works. To measure your material by weight, you will need an accurate scale. Since most of our liquid urethane rubbers are 1A:1B by volume, some users find it easier to measure their material that way. If you have a proportioner that automatically mixes large quantities of your material when needed, following the mix ratio by volume is usually the way to go.