Abstract: An air filter unit is provided for use with an internal combustion engine. The unit includes inner and outer sleeves, a filter medium disposed intermediate the sleeves, and end plates affixed to and overlying the corresponding ends of the sleeves and filter medium. At least the outer sleeve is formed from a blank of foraminous, relatively stiff, sheet material with the periphery thereof including burr-forming peripheral portions and an elongated peripheral portion folded back upon itself to form a hem-like segment. The blank is then formed into a cylindrical sleeve with the hem-like segment overlapping and being affixed to a burr-forming peripheral portion opposite the hem-like segment so as to form an elongated seam extending the length of the sleeve. The overlapped seam-forming peripheral portion being exposed only on an interior surface of the sleeve.