I just received a circa 1900 German violin and was immediately struck with the provided case.  Evidently a mold was used for both the case body and top.  Concrete impregnated cloth layers were placed in the molds and allowed to dry.  The exterior was painted black and has the texture of the underlying cloth.  Very rigid and inexpensive method of construction.  The interior is conventional (for the period) glued on cloth.  Without using a scale, it seems slightly heavier than cloth over wood but not at all objectionable.  I am quite impressed with it.

The thus protected violin was in wonderful condition.