Brady M21-375-C-342 The B-342 Polyolefin PermaSleeve material is a non-adhesive, heat-shrinking sleeve that fits around wires or cables for easy permanent identification. 3:1 heat-shrinking wire sleeve is ideal for labeling in harsh environments and is resistant to chemicals, grease, oil and cleaning agents. Polyolefin wire marking sleeves have a smudge-proof finish and print in black text on a white background.