The composition and concentration of soap determine its foaming capacity. Equal volumes of solutions from different samples with the same concentration can be compared by shaking them for the same amount of time with the same force. After that, the solutions are left to rest until the froth formed by shaking has evaporated. In each sample, the time it takes for the foam to disappear is calculated. The greater the foaming capacity or cleaning activity of a soap sample, the longer it takes for the foam to dissipate.

This video explains the foaming capacity of different samples of soap.