High Temperature Sleeving: Fiberglass vs Silicone vs PTFE/FEP Material Selection
When a harness or motor lead runs above 125 °C, ordinary polyolefin falls out of the spec and you are choosing among fiberglass constructions, silicone-coated tubes, fluoropolymers and polyimide. This guide sets out the continuous and short-term limits, the failure modes that matter, and the decision sequence we use when sizing a high-temperature sleeving.
1. Continuous vs Short-Term Temperature: Read the Right Number
Every high-temperature sleeving data sheet carries a temperature figure, but they are not all the same. A 260 °C flash / short-term rating is not a 260 °C continuous rating. When a motor lead or an oven harness runs hot for hours, you size on the continuous figure with margin, and treat the short-term peak as an overload tolerance, not a normal running condition.
| Material | Continuous temp | Short-term peak | Primary strength | Primary limit |
|---|---|---|---|---|
| Bare fiberglass braid | ~155-180 °C | 260 °C | Low cost, dielectric | Frays, low abrasion |
| Silicone-coated fiberglass | 200-260 °C | 300-400 °C | Flexible, abrasion | Chemistry, cost |
| Extruded fiberglass sleeve | ~200 °C | 260-300 °C | Stiff, high dielectric wall | Bending radius |
| PTFE (heat-shrink or tubing) | -70 to 260 °C | ~300 °C | Chemical, non-stick, dielectric | Cost, cold-flow |
| FEP | -60 to 200 °C | ~230 °C | Smooth, meltable for sealing | UV, cost |
| PFA | -60 to 260 °C | ~280 °C | Higher strength than FEP | Cost |
| Polyimide film | ~260 °C | ~400 °C | Thin, high dielectric | Soft, abrasion-poor |
Rule of thumb: for a continuous hotspot above 125 °C, move out of polyolefin; above 200 °C, restrict to silicone-coated fiberglass, fluoropolymers or polyimide; and confirm the number against the exact specification you plan to cite.
2. Abrasion, Bending and Chafe: The Mechanical Layer
High temperature is rarely the only requirement. Vibration, edges and repeated flexing are what actually destroy a sleeving in service. Silicone-coated fiberglass has the best balance of flexibility and abrasion resistance, which is why it dominates motor and harness applications. Bare fiberglass braid frays at cut ends — the cut edge must be sealed or the fibre irritating. Extruded fiberglass is stiffer and holds a round cross-section well but needs a larger bending radius.
- For running chafe and flex, prefer silicone-coated fiberglass or a braided textile layer.
- For a fixed, straight section needing a rigid dielectric wall, extruded fiberglass sleeve works.
- Check the cut-edge treatment: sealed ends beat raw fiberglass on a moving harness.
3. Chemical and Environmental Compatibility
Solvents, oils, fuels and cleaning agents change the answer. Fluoropolymers (PTFE/FEP/PFA) resist the widest chemistry and are impermeable, so they win in chemical plant and aggressive washdown. Silicone-coated fiberglass tolerates many hydrocarbons but not all aggressive solvents at elevated temperature. Confirm the specific contaminate, concentration and temperature against the material data, not against a general 'resistant' claim.
4. Dielectric and Insulation Contribution
Where the sleeving also carries an electrical duty, dielectric strength and wall thickness matter. Extruded fiberglass and fluoropolymer walls offer higher per-millimetre dielectric than a thin open braid. Note that rated operating voltage depends on the actual wall and the air gap, so state the intended voltage class when specifying, and pair with the product page data where a specific product wall is quoted.
5. Selection Decision Sequence
- Define the continuous hotspot temperature and the short-term peak.
- Define the environment: chemicals, oil, water, UV, washdown frequency.
- Define the mechanical duty: fixed vs moving, edges, bending radius, abrasion.
- Define any dielectric / voltage class requirement and the wall thickness available.
- Match to a material family, then to a product wall and cross-check the certification file.
Related: Silicone Coated Fiberglass Sleeve · Extruded Fiberglass Sleeve · PTFE/FEP/PFA Heat Shrink · High-Temperature Sleeving for Industrial Equipment
Frequently asked questions
What is the highest continuous temperature a fiberglass sleeving handles?
Bare braided fiberglass tolerates roughly 155-260 °C continuous depending on coating and weave; a silicone-coated version handles 200-260 °C continuous with short peaks to 300-400 °C. Size on the continuous figure, not the flash rating.
When should I pick PTFE or FEP over silicone-coated fiberglass?
Choose fluoropolymers when you also need chemical resistance, lowest friction, an impermeable wall and tighter tolerances. Choose silicone-coated fiberglass for flexibility and abrasion at lower cost when temperatures stay within 260 °C and chemistry is mild.
Does 'high temperature rated' mean the sleeving is also flame retardant?
No. Temperature rating and flame retardancy are separate. A sleeving rated 260 °C can still feed a flame front; check the vertical flame test and UL rating separately.
Can I use polyimide film sleeving for abrasion protection?
Polyimide film excels at dielectric strength in thin sections but has a soft surface. For rubbing and chafe, silicone-coated fiberglass or a braided textile is the better wear layer.
Unsure which high-temperature sleeving fits your hotspot?
Send the continuous temperature, chemical exposure and mechanical duty. We return a material recommendation with data sheets.
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