I think that they were just lightweight cotton soaked in Linseed oilDo they still make oilskin capes? Mine is around 30 years old and needing replacement fairly soon. It weighs a ton (well, perhaps a couple of kilograms) but that's what makes it so good - it doesn't flap all over the place in the wind like the flimsy polythene capes you see nowadays that make people say capes are a waste of time. I tried one and threw it away - the old fashioned ones are brilliant.