TamSeal BBR is a pre-formed, hydrophilic waterstop consisting of sodium bentonite and butyl rubber. It will swell up to 750% when in contact with fresh water. When fully encapsulated by poured concrete, the expansive forces form a seal against the concrete surfaces. This seal resists hydrostatic pressure, stopping water from entering the sub-structures. TamSeal BBR is able to withstand a 40 metre head of pressure. As with any hydrophilic waterstop, TamSeal BBR will return to its original size if the concrete and substrate is completely dry and no more moisture is present. If water or moisture is introduced again, TamSeal BBR will re-expand.