GJ, The OZ Gedney type "S" Cable support is made of impregnated hardWOOD. What will they think of next??
The type "D",(split, so it can be used in existing installations), and type "R" (that you pull the wires through) are made of phenolic resin. Hope you ordered the former, 'cause the type "R" looks like a real pain in the %!*< to install.