Brake dust plate gasket

Hi all, nearly finished refurbing the front end of my 77 Dodge Tradesman. When I removed the brake dust plates they had a thin foam like gasket between them and the steering knuckle. I've never seen this in the UK before? Do any of you know what the gasket is made of and is it necessary for my rebuild?
Cheers, Timbo. 👍
Author: Timbo