What were world war 1 helmets made from?

Originally Germany entered the war in 1914 with a leather helmet with a spike atop it, called the Pickleshube(sp?). This was replaced in 1916 by their coal scuttle shaped M1916 all steel helmet. France produced their own all steel Adrian helmet, and the US adapted the British all steel Tommy helmet (also known as the Brodie, and later the Model 1917 "dough-boy" helmet).