PTFE vs Graphite Packing for Valves

Valve stem packing controls fugitive emissions and leakage at the bonnet. The two materials buyers weigh most often are PTFE (polytetrafluoroethylene) and flexible graphite. Both seat well and both are staples of modern valve service — but they are not interchangeable.

PTFE packing for valves

Chemical inertness: PTFE resists almost every acid, caustic and solvent, and is food- and pharma-grade (FDA 21 CFR 177.1550).
Low friction: it seals at low gland stress, which is gentle on the stem and easy for field crews to tighten.
Limit: PTFE begins to soften and cold-flow above roughly 260 °C, so it is a poor choice for hot steam or thermal-cycling valves.

Graphite packing for valves

Temperature: flexible (expanded) graphite stays stable to about 500 °C and handles steam, hot oil and thermal swings far better than PTFE.
Low leakage: with correct gland stress (often via live-loading) graphite achieves the tight emission limits referenced in standards such as ISO 15848-1.
Fire-safe: graphite does not burn, supporting防火 requirements such as API 607.
Trade-off: it needs higher compression to control leakage and can oxidize in strong oxidizers (e.g. concentrated nitric acid).

Side-by-side

Factor	PTFE	Graphite
Max service temperature	~260 °C	~500 °C
Chemical range	Broadest inertness	Excellent, avoid strong oxidizers
Gland torque needed	Low	Higher
Steam / hot service	Not recommended	Preferred
Best for	Chem, food, pharma, low-temp	Steam, high-heat, emission-critical

How to decide

Pick PTFE when the media is aggressive chemicals at moderate temperature and you value easy installation. Pick graphite when the valve sees steam, high heat, or must meet strict leakage/emission limits. See also our PTFE vs graphite material overview and the valve stem packing guide.

Frequently Asked Questions

Which is better for steam valves, PTFE or graphite?

Graphite. PTFE softens and cold-flows above about 260 °C, so it is unreliable on steam service. Flexible graphite remains stable near 500 °C and is the standard choice for steam and hot-oil valves.

Is graphite packing fire-safe?

Yes. Expanded graphite does not burn and is widely used where fire-safe performance is required (e.g. API 607). PTFE decomposes and can release fumes at high temperature.

Why does graphite need more gland torque than PTFE?

Graphite is less elastic than PTFE, so the gland must apply higher, well-distributed stress to close leakage paths. Live-loading the bonnet helps hold that stress as the packing relaxes.

Can I use PTFE packing on a chemical valve that also sees heat?

Only if the temperature stays at or below roughly 260 °C. If the valve cycles hot, choose graphite or a graphite-PTFE composite that balances chemical resistance with heat stability.