Heat shrink ratio 2:1 or 3:1 - which fits your cable?

What does the shrink ratio mean?

The shrink ratio is the relationship between the supplied expanded diameter and the smallest achievable recovered diameter. At 2:1 the tubing shrinks to half its size, at 3:1 to one third of the expanded diameter.

A 2:1 tube with a 12 mm expanded diameter recovers to a minimum of 6 mm. A 3:1 tube with the same starting size reaches around 4 mm. The larger the ratio, the wider the span between sliding on loosely and gripping tightly.

When to choose 2:1 versus 3:1?

2:1 is the standard for straight cables, strands and uniform diameters. 3:1 shows its strength when large steps in diameter have to be bridged, such as at connectors, ferrules or cable transitions.

• Choose 2:1 when the start and end diameters are close together.
• Choose 3:1 when a thin cable steps up into a thick connector.
• Use adhesive-lined tubing (usually 3:1) where a seal against water or oil is required.
• Mind the wall thickness - thin wall insulates, thick wall protects mechanically.

How do I calculate the expanded diameter?

Rule: the expanded diameter should be about 20 % larger than the thickest object to be covered so the tube slides on easily. The recovered diameter must be smaller than the thinnest object so it grips firmly.

Example cable transition: thin cable 4 mm, thick connector 9 mm. You need an expanded diameter of at least 9 mm plus clearance, so about 11 mm. A 2:1 tube of 11 mm recovers only to 5.5 mm, too loose for 4 mm. A 3:1 tube of 12 mm reaches 4 mm and seats cleanly. That is why 3:1 wins here.

Frequently asked questions