... is made of fire-retardant PVC material and spring steel ring, a Flexible DuctProduct DescriptionVentiductStyle: Bugle style, portable style, straight ... is made of fire-retardant PVC material and spring steel ring, and it is able to endure the high temperature, ... it can fix the flexible duct expediently, there is a metal ring per meter, so it can connect the ventilator discretionarily, the ...