10'' yellow polypropylene block (not detectable), filled stiff gray metal detectable and X-ray visible polyester. Should fibers come away from the brush and get into a production line, they will likely be detected by most correctly calibrated metal detection systems. Ask us for sample fibers to conduct your own tests. The angled material at the sides and front of this rugged, durable bush is superb for cleaning in hard-to-reach corners, while the gripped handle is comfortable to use even in gloved hands. See also the D4RESMDX, with a detectable block, as well as fibers.