PTFE is widely described as having "near-universal" chemical resistance — but near-universal is not universal. Understanding exactly what PTFE resists, what it does not, and how operating temperature interacts with chemical attack is essential for safe, compliant fluid system design.
Why PTFE Is So Chemically Resistant
PTFE's chemical inertness derives from the carbon-fluorine bond — one of the strongest bonds in organic chemistry (544 kJ/mol). The fluorine atoms completely sheath the carbon backbone, presenting a surface that virtually no chemical can attack. There is no hydrogen to substitute, no oxygen to oxidise, no double bond to add across. It is this structural reason, not a surface coating, that gives PTFE its resistance — it is intrinsic to the material throughout.
What PTFE Resists
- Strong mineral acids — hydrochloric (HCl), sulphuric (H₂SO₄), nitric (HNO₃), hydrofluoric (HF) at all concentrations and temperatures.
- Inorganic bases — sodium hydroxide (NaOH), potassium hydroxide (KOH), ammonia solutions.
- Organic acids — acetic, formic, oxalic, and other carboxylic acids.
- Organic solvents — ketones, esters, ethers, aromatics, chlorinated solvents, alcohols, aldehydes.
- Oxidising agents — hydrogen peroxide, sodium hypochlorite, chromic acid.
- Fuels and hydrocarbons — gasoline, diesel, jet fuel, lubricating oils at all concentrations.
What Can Attack PTFE
Temperature Performance
| Temperature Range | Performance Notes |
|---|---|
| –200°C to –65°C | Cryogenic service — PTFE remains flexible (unlike rubber, which becomes brittle) |
| –65°C to +150°C | Standard operating range — full mechanical and chemical properties maintained |
| +150°C to +200°C | Elevated service — pressure ratings begin to derate; verify with engineering data |
| +200°C to +260°C | High-temperature service — significant pressure derating; short-term exposure only |
| Above +260°C | Thermal decomposition — not serviceable; hazardous fluorocarbon gases may be released |
FEP and PFA in Edge Cases
Where optical clarity is required (flow visualisation, UV transmission), FEP or PFA is preferred over opaque PTFE. PFA offers PTFE-equivalent chemical resistance and temperature range (continuous to 260°C) with superior flex life and optical clarity — the standard choice for semiconductor ultra-pure chemical delivery and pharmaceutical WFI distribution where PTFE's opacity is a constraint. FEP is slightly less temperature-capable (continuous to 200°C) but offers better optical transmission and is melt-processable for complex geometries.