APL-R, APL-C and APL-M heat shrink kits are specially made per a design developed in 1973 by Crouse-Hinds, Raychem and Brad McCann of Isbill Associates. It was exhaustively tested by them to prove water resistance for extreme environmental conditions. It was commonly referred to as "the Raychem heat shrink kit" though we can make it with Raychem, Canusa or 3M tubing. Any of the styles contain a separate Raychem special adhesive that is like tar and never gets hard. It adheres strongly to the cable and the heat shrink tube. Common kits in the industry use a painted on adhesive inside the tubing. That adhesive, from our experience and some airport experience, does not adhere to the cable or tube and can leak over time through the cracks that appear around the sealant.