Our 3:1 adhesive lined (Dual Wall) heat shrink pre cut pieces is also available with a "dual-wall" construction. It is called dual wall because it is actually made up of two different materials together. One wall - the outer wall - is Polyolefin heat shrink. The second wall (hence the name "dual wall") - the inner wall - is a hot melt adhesive. When exposed to heat (usually a bit lower than the activation temperature of the heat shrink), the inner layer begins to flow (just like a hot melt glue). When the tubing shrinks and cools down, inner layer forms an adhesion layer between the tubing and the component or wire. This provides a water-tight seal, protecting the connector and/or wire. It also allows the tubing to stick to the substrate. This is why this tubing is also called adhesive lined heat shrink tubing.