What is the thickness of the fire-rated duct? A fire-rated duct ought to be built with a single pores and skin, getting a complete thickness not exceeding 2mm. This measurement consists of the intumescent coating, which is important for improving fire resistance. In accordance with the World Well being Organisation https://fire-resisting-ductwork-s34556.bcbloggers.com/38236046/fire-rated-ductwork-things-to-know-before-you-buy