The Duct to Duct Increaser connects 3 in. to 4 in. ducts together. It is ideal for bathroom fan exhaust applications. Finished in black color. The increaser is designed to be a tight fit to reduce air leaks in the connections. When using the increaser with a 3 in or 4 in snap pipe aluminum or galvanized , it may be necessary to unsnap the receiving end of the pipe, then insert the increaser and snap the pipe back together.Made of polypropyleneUsed when your exhaust port or exhaust hood needs to be increased from 3 in. to accommodate a 4 in. ductConsult your local building codes for approved installation practicesLight weight design