Heat Shrink Tubing 2:1 Ratio — φ3.5 to φ6mm Electrical Insulation Cable Sleeve

Measure the outer diameter of the wire or connector you need to cover, then select a tubing size that is slightly larger before shrinking. With a 2:1 ratio, the tubing shrinks to approximately half its listed diameter. For example, φ4mm tubing will shrink down to roughly 2mm, so it works well on wires up to about 1.8–2mm in diameter. When in doubt, size up by one step.

Quick reference (approximate): φ3.5mm → 20–22 AWG | φ4mm → 18–20 AWG | φ4.5mm → 16–18 AWG | φ5mm → 14–16 AWG | φ6mm → 12–14 AWG.

A 2:1 shrink ratio means the tubing will shrink to approximately half its original inner diameter when heat is applied. This is the most common ratio for general electrical insulation and wire bundling tasks. If you need a tighter seal — for example, over a connector with a larger flange — a 3:1 adhesive-lined tubing may be a better fit.

Polyolefin heat shrink tubing generally begins to shrink at around 70–90°C (158–194°F) and fully recovers at approximately 120°C (248°F). A heat gun set to low or medium is the recommended tool. A lighter can work in a pinch but may cause uneven shrinkage or scorching — move the flame continuously and keep it at least 2–3 inches from the tubing.

Polyolefin tubing is generally resistant to moisture, UV exposure, and common automotive fluids, making it suitable for most outdoor and under-hood wiring applications. For fully waterproof connections — such as trailer wiring or marine below-deck runs — consider adhesive-lined (3:1) tubing instead, which creates a sealed bond around the wire.

Yes. Heat shrink tubing is commonly used to insulate and protect solder joints, crimp terminals, butt connectors, and exposed wire ends. Select a diameter that slides freely over the connector body before shrinking. For larger connectors, check our φ6mm option or our wider-diameter listings.

No. Color is purely for identification and organization — for example, using red for positive leads and black for negative, or color-coding individual conductors in a multi-wire harness. All color variants share the same electrical insulation properties and shrink performance.

Slide the tubing over the connector before applying heat — it should pass over the widest point with a little clearance. If it won't slide on, you need the next size up. In most cases, choosing a diameter 20–30% larger than the connector's widest point gives a clean, wrinkle-free result after shrinking.