A flexible container breakwater "FCB", is made of a flexible membrane which filled with sand-water slurry. It is proposed for use in shallow water to attenuate wave energy in non-frequent storm sites and as temporary deployments, instead of costly traditional breakwaters. Experimental studies were carried out under irregular waves mainly in a wave flume and another limited runs in a wave basin. The purpose is to evaluate FCB stability criteria and wave dissipation capabilities. Filling the FCB with slurry with 40% sand was found safe enough against floatation forces. Also, It keeps the system in position under subaerial condition at Hs=1.50 m &Tp=5.5 s and Hs=1.9 & Tp=7.0 s waves according to the FCB bottom contact width. For higher waves, it need be moored by a belt in which the maximum total force is estimated as 2% of its net weight under subaerial conditions and 4% under submergence ratio 0.15. The dissipation coefficient, within the tests program, reached to 80%. Finally, important parameters affecting the efficiency were discussed and its range of applications was proposed.