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24
Sep
In short: To size heat shrink tubing, work with two diameters: the expanded (supplied) size must slip over the largest part it has to pass, and the recovered (fully shrunk) size must be smaller than the object it grips. Choose a tubing whose expanded diameter is about 20–30% larger than the object and whose recovered diameter is smaller than it. Shrink ratio (2:1, 3:1, 4:1) tells you how far the tubing shrinks — higher ratios suit irregular shapes and connectors.
How Heat Shrink Sizing Works
Expanded vs Recovered Diameter: Heat shrink tubing has two key sizes. Expanded (or supplied) diameter is its size before heating — it must be large enough to slide over the object. Recovered diameter is its fully shrunk size — it must be smaller than the object so the tubing grips tightly. The ratio between them is the shrink ratio.
Sizing tubing by one number is the classic mistake. You always need two: it has to go on, and it has to grip. Polyolefin is the most common material, balancing flexibility, shrink performance, and cost.
| Term | Meaning | Sizing Rule |
|---|---|---|
| Expanded diameter | Size as supplied | ≥ 20–30% larger than object |
| Recovered diameter | Size after full shrink | Smaller than object to grip |
| Shrink ratio | Expanded ÷ recovered | 2:1, 3:1, or 4:1 |
How to Measure and Choose a Size
Measure the largest diameter the tubing must pass over (a connector, a splice, a plug) and the diameter of the object it will finally grip. Choose tubing whose expanded size clears the first and whose recovered size is smaller than the second. Representative sizing:
| Application | Object Diameter | Suggested Expanded Size | Ratio |
|---|---|---|---|
| Single small wire | 1–3 mm | 3/32” – 1/8” | 2:1 |
| Standard wire / joint | 3–6 mm | 3/16” – 1/4” | 2:1 |
| Connector / lug | 6–12 mm | 3/8” – 1/2” | 3:1 |
| Irregular / large splice | 12–25 mm | 3/4” – 1” | 3:1 – 4:1 |
When in doubt between two sizes, choose the smaller expanded size that still clears the largest part — it grips more tightly once recovered.
Shrink Ratios Explained
The shrink ratio tells you how much the tubing reduces. Higher ratios shrink further from the same starting size, which is what lets one piece pass over a bulky connector and still grip a thin wire behind it.
| Ratio | Shrinks To | Best For |
|---|---|---|
| 2:1 | Half of expanded diameter | Straight wire runs, uniform diameters |
| 3:1 | One-third of expanded diameter | Connectors, lugs, stepped diameters |
| 4:1 | One-quarter of expanded diameter | Irregular shapes, large-to-small transitions |
Adhesive-Lined vs Standard Tubing
Standard heat shrink tubing insulates and bundles. Adhesive-lined (sometimes dual-wall) tubing has an inner adhesive layer that melts on heating and flows into gaps, creating a moisture-tight seal and adding strain relief. Use adhesive-lined tubing for outdoor, automotive, and marine splices where water ingress or vibration is a concern; use standard tubing for general indoor insulation and identification where a seal is not required.
Applying Heat Shrink Correctly
Slide the tubing into position before powering or connecting anything — it cannot be added later without disassembly. Apply heat evenly with a heat gun, working from the centre or one end toward the other so trapped air escapes, and rotate around the circumference for even shrink. Avoid an open flame: it scorches the tubing, weakens it, and shrinks unevenly. Stop heating once the tubing has fully conformed; over-heating can split or char it. For adhesive-lined tubing, heat until a small amount of adhesive just appears at the ends, confirming the seal.
Conclusion
Sizing heat shrink tubing comes down to two diameters and one ratio: it must slide over the largest part, grip the object once recovered, and shrink far enough to do both. Add an adhesive lining when you need a seal, heat it evenly with a gun rather than a flame, and stop once it has conformed.
Shop heat shrink tubing by size, ratio, and type at cabletiesupply.com/collections/heat-shrink-tubing. Free shipping over $99, free returns. Questions on sizing? Call 866-455-8437.
