Very thick, impermeable, inflexible fabric that has been treated with some chemical. Windproof, but not insulating, and very heavy and stiff.
Hoods appear to be lined with shirt weight wool material. They are less stiff than the smocks and trousers, likely because the material was not impregnated.
Some mix Brushstroke and Moon and Balls fabrics.
Besides officially being used by Belgians in the Congo, a few items were used in Rhodesia, though this was not typical.