Heat Shrink Tubing Shrink Ratio
A shrink ratio is one number from one dimension: how far the inside diameter drops when the tube recovers. It tells you nothing about voltage, sealing or temperature. This guide explains supplied ID vs recovered ID, walks a 7-step sizing workflow, and lists which Wellele SKUs publish which ratios.
Supplied ID, recovered ID and the ratio
Heat shrink tubing is delivered in an expanded state. Three numbers describe the sizing:
- Supplied ID : the inside diameter as shipped. The tube must slide over the largest object in the assembly, so this is the fitting dimension.
- Recovered ID : the inside diameter after full, free recovery on nothing at all. This is the gripping dimension; it must end up smaller than the part it should clamp.
- Shrink ratio : supplied ID divided by recovered ID. A 3:1 tube with a 6.0 mm supplied ID recovers to about 2.0 mm; a 3:1 tube with a 12.0 mm supplied ID recovers to about 4.0 mm. Same ratio, different grip.
Wall thickness also changes: the recovered wall is thicker than the supplied wall by roughly the same factor. Recovery happens in two stages: the ID drops quickly as the cross-link memory takes over, then full recovery needs enough heat held long enough. Under-heated tubing stops partway and never grips.
How to size a heat shrink ratio in 7 steps
- Measure the largest assembly OD. Identify the biggest object the sleeve must pass over : connector backshell, lug barrel, splice body, or molded transition.
- Pick a supplied ID above it. Leave slide clearance, typically 10–20% over the measured OD. Too tight risks tearing on insertion; too loose wastes recovery travel.
- Identify the smallest grip target. Find the smallest continuous diameter the recovered tube must clamp : usually the cable jacket or wire insulation just past the bulge.
- Compute the required ratio. Supplied ID ÷ desired recovered ID, then keep margin: size the recovered ID roughly 15–25% below the part so the tube bites instead of resting loose.
- Check wall and heat limits. Confirm the recovered wall meets the insulation or abrasion requirement, and that the full-recovery temperature will not damage soldered joints, adhesives or connectors in the assembly.
- Confirm certification needs. Match the required approvals on the product page : UL 224, flame class, halogen-free : before locking a size, since not every ratio exists in every certified range.
- Check the environment. Continuous temperature, chemical or fluid contact, UV and flexing decide the material family; ratio only decides the fit. If the environment is severe, go back to the materials hub and re-shortlist.
What a shrink ratio does not tell you
Do not specify by ratio alone. The ratio says nothing about:
- Voltage rating. Electrical class comes from the material system and wall construction, not from how far a tube shrinks. A 4:1 tube is not "more insulating" than a 2:1 tube. Group products by electrical class on the voltage rating page instead.
- Sealing. Only adhesive-lined dual-wall constructions seal; the ratio is unrelated to whether moisture is blocked.
- Temperature and chemical resistance. These follow the polymer : polyolefin, silicone, PVC or fluoropolymer. Compare families on the materials page.
- Flame performance. Flame class is a compound property, independent of ratio.
A ratio also assumes free recovery. On real parts, recovery stops at whatever it first grips, so a sleeve placed over a bulge may recover unevenly. That is expected behavior, not a defect. It is why step 4 keeps grip margin.
Published shrink ratios on Wellele SKUs
Only the products below state a numeric shrink ratio on their own specification pages. Sizes differ per family; the ratio line is what these families share.
Products without a heat-shrink ratio
Not every sleeve on this site recovers by heat, so the ratio metric does not apply to them. Cold shrink accessories are held pre-stretched on a removable core and grip as the core unwinds: no heating step, no supplied/recovered ID pair. Braided and woven sleeves slide or wrap over the part at any point in the build. Self-amalgamating and composite tapes build insulation by wrapping, not by shrinking. These are organized by type on the product types page and by electrical class on the voltage rating page; a few common examples:
Frequently asked questions
How do I choose between 2:1, 3:1 and 4:1?
Measure the largest object the tubing must slide over and the smallest surface it must grip. Divide supplied ID by the target recovered ID and pick the smallest ratio that clears the bulge and still grips with 15-25% compression. 2:1 suits straight runs and simple steps; move to 3:1 or 4:1 when a connector bulge must clear and recovery lands on thin wire.
Why is recovered ID more important than ratio alone?
The recovered ID is the diameter the tube actually holds after full recovery - it is what grips your part. Two 3:1 tubes with different supplied IDs recover to different sizes, so a ratio headline without a size table cannot tell you whether a sleeve will clamp correctly. Confirm supplied and recovered ID from the size table before specifying.
Can a higher ratio always replace a lower ratio?
No. A higher-ratio tube is supplied with a thicker expanded wall, shrinks more along its length, thins more on recovery and usually costs more. On a straight cable run a 2:1 often gives a neater and cheaper fit. Step up only when a physical bulge demands it, then confirm the recovered wall still meets your insulation requirement.