How to Choose Heat Shrink Tubing for Wire Harness

Wire harness protection is the largest use case for heat shrink tubing. The right sleeve keeps a bundle neat, marked and insulated against abrasion, fluids and heat. This checklist walks a procurement or harness engineer through the four numbers that decide the part.

1. Pick the base material

Most harnesses use polyolefin heat shrink for its balance of flexibility, dielectric strength and cost. Where flame safety or low smoke matters (rail, transit, enclosed cabinets) move to halogen-free tubing. For tight bends and printed markings, PVC shrink is a common, economical choice.

2. Match the shrink ratio to the bulge

The shrink ratio is supplied ID ÷ recovered ID. A 2:1 ratio covers modest steps; if one sleeve must pass over a connector barrel and then grip a bare wire, ask for 3:1 or 4:1. See our guide on heat shrink by performance for the full ratio range we keep in stock.

3. Size to the cable OD, not the wire

Measure the largest diameter the sleeve must slide over (connector, lug, splice). Supplied ID must clear it with a few millimetres to spare; recovered ID should grip the smallest section. When in doubt, size up one step rather than force a tight fit. Dual-wall adhesive versions seal the gap and resist tracking.

4. Choose the wall and adhesive

Thin wall for dense bundles where space is tight; medium or heavy wall where mechanical abuse is expected. For outdoor, buried or washed-down harnesses specify adhesive-lined (dual-wall) so the melt adhesive blocks moisture.

What to send us

Cable OD, voltage class, operating temperature, environment and quantity. We return a sized recommendation with the stock code and spec sheet. Browse the full range in products by application.

The four numbers at a glance

1. Base material: polyolefin for most harnesses, halogen-free where flame safety or low smoke applies, PVC for tight bends and printed marking.
2. Shrink ratio: 2:1 for modest steps, 3:1 or 4:1 when one sleeve must pass a connector and then grip a thinner section.
3. Cable OD: size to the largest diameter the sleeve slides over, then check that the recovered ID grips the smallest section.
4. Wall and adhesive: thin wall for dense bundles, medium or heavy wall under mechanical abuse, dual-wall where moisture or washdown is present.

Frequently asked questions