Sepn. of gas contained in foam bubbles from the liq. phase was explained by breaking the foam lamellas under load. According to the literature (A. Vrij, J.J. Overbeck, 1968) and authors' own unpublished data, the tensile stress was found responsible for the effectiveness of the lamella breaking at the resp. dynamic interfacial tension level. A lamella breaking parameter < 0.1 > was introduced to the math model describing the foam destruction. A good agreement of the calcd. and exptl. was obsd.