Hydrophilic composite structures are made by impregnating a 3DL structure with a polyurethane foam formulation and curing the formulation to produce a foam that occupies the spaces in the 3DL structure. The composite structures have an unusually good capacity for retaining water even when under compressive forces. They also exhibit at most moderate swelling when saturated with water. The foam is useful as a layer of a water containment system such as a green roof or blue roof system.