One of our best clients is the company that invented this type of material and is the largest manufacturer of it in the world. The material is made of a mixture of wood flour mixed with plastic resins and binders that are then extruded to form the sheets. This stuff is durable, stable, and very enviro friendly in that it uses mostly waste material (i.e. saw dust from mills) that would otherwise be thrown away.
By the time it is shot, you will be ready for a new tub anyway.
Regards,
Bill