Basicly, cuir boulli is a heat treatment for leather. In translation, it means boiled leather, but there are less aggresive ways of doing it. The process hardens the leather short of making it brittle, and it takes on some of the properties of rawhide, in that it is hard, but in most cases, retains some flexability. In earlier history it was used in making light armor. The basic process is to dampen the leather just as you would for carving or molding, then heat to around 130° to 140° until thoroughly dry. It CAN be done by intense sun exposure.