Rats, mice, birds and insects getting in through holes Stuf-Fit copper mesh is the answer to all your exclusion problems! Unlike steel wool, Stuf-Fit does not rust and is made of the finest ingredients such as brass, copper and other inert metals. It is rustproof, stainproof and works great to seal weepholes and around plumbing, A/C, vents, and other places where rodents and insects enter. Simply use a pair of scissors and cut off the amount you need.