Specific impulse
Specific impulse is also used to describe how well model rocket motors work. In the table below are some of Estes' claimed values for specific impulses for several of their rocket motors: Estes Industries is a large, well known American seller of model rockets and rocket parts. The specific impulse for model rocket motors is much lower than for many other rocket motors because the black powder is used as a fuel. Black powder is used in model rocket motors because it costs less.