Silicone surfactants (surface-active materials) are essential and therefore used in the production of all kinds of PU foam. They lower surface tension, emulsify incompatible formulation ingredients, promote nucleation of bubbles during mixing, stabilize the rising foam by reducing stress concentrations in thinning cell-walls and counteract the defoaming effect of any solids added to or formed (e.g. precipitated polyurea structures, during conventional flexible foam reaction).