Abstract: A device for forming an orthopedic cast is disclosed which is composed of a core having a fibrous, porous tape rolled thereabout. The tape is impregnated with a first liquid component of a two-component hardenable system. The core is composed of a pressure rupturable container having the second component of the two-component system therein in liquid form. The entirety is encased in a flexible package which serves as a mixing chamber for intermixing the first and second components upon application of pressure to the package sufficient to rupture the core. After intermixing, the package is opened, the tape unrolled and placed about the broken limb in the conventional manner. The cast hardens within a short time at ambient temperature to provide a light-weight, breathable and waterproof orthopedic cast.