PTFE packing is the chemical-resistance and low-friction workhorse, rated across the full 0–14 pH range, with a service temperature of roughly −300 °F to +500 °F (−184 °C to +260 °C) and a practical shaft-speed ceiling near 1,200 fpm [S1]. Graphite packing, by contrast, runs from about −400 °F to +850 °F (−240 °C to +454 °C), has effectively no shaft-speed ceiling, and dissipates frictional heat through the gland instead of trapping it [S1].
Both materials are post-asbestos braided constructions used to seal gland packing in rotating and reciprocating equipment. The decision is driven by four parameters: media chemistry, temperature, shaft speed, and PV (pressure × velocity) duty, plus the less obvious question of whether the service is wet, dry, or steam-dominant [S1][S4].
Material Construction and Why It Matters
Flexible (expanded) graphite packing is made by oxidising natural graphite flake with sulfuric and nitric acids and then exfoliating it with heat, producing a wormlike, layered structure that is re-compacted into yarns, tapes, or braided packings [S1]. Pure braided graphite typically carries 95%+ carbon content and is inherently self-lubricating, which is why it can run dry or with minimal flush water [S1].
PTFE packing, by contrast, is a synthetic fluoropolymer of tetrafluoroethylene (the same base resin sold as Teflon) supplied as 100% PTFE yarn, PTFE impregnated with a lubricant, or a multifilament yarn dip-coated in PTFE dispersion [S1][S2]. The C–F bond in PTFE is one of the strongest single bonds in organic chemistry, which is the molecular reason behind its near-universal chemical inertness [S4].
Hybrid constructions are common in real plants: aramid-cored PTFE-graphite packings combine a tough aramid core with a PTFE/graphite jacket to reduce gland wear and ease break-in, and graphite yarns are routinely treated with PTFE to stop black colour transfer into the process fluid [S2][S5].
Spec-by-Spec Comparison: PTFE vs Graphite Braided Packing
The headline numbers from manufacturer and distributor data line up cleanly across sources. PTFE tensile strength is around 2,000 PSI versus roughly 650 PSI for graphite packing, but tensile strength is rarely the limiting parameter in a stuffing box; thermal behaviour is [S1].
Two engineering consequences fall out of that table. First, PTFE's low thermal conductivity and high thermal expansion coefficient mean heat builds up at the shaft interface; in higher-speed pumps this drives running torque up and forces the user to add a flush or cooling plan [S4]. Second, graphite's high thermal conductivity pulls heat out of the contact zone, which is exactly why it is the default material in steam turbines, high-temperature valves, and high-duty refinery pumps [S1][S4].
Where PTFE Packing Wins, and Where It Fails
PTFE braided packing is the right call when the process fluid is aggressive, the shaft speed is moderate, and colour transfer or contamination cannot be tolerated. Typical fits are strong acids, alkalis, solvents, oxidisers (excluding molten alkali metals), mineral and synthetic oils, fuel gases, and pharmaceutical or food media where FDA-grade multi-yarn PTFE constructions are specified [S2]. It is also the cleaner choice for control valves, where a low friction coefficient reduces hysteresis and improves actuator repeatability, and for any application where sleeve or stem wear is a recurring cost [S4].
The failure modes are equally specific. PTFE starts to carbonise above ~500 °F (260 °C), so it is the wrong material for superheated steam headers, hot oil above its thermal limit, or any high-PV pump running without a flush [S1][S4]. Small molecules (chlorine, some refrigerants) can permeate plain PTFE constructions over time, so permeation risk has to be reviewed against the service even when bulk chemistry looks fine [S4]. In governor glands on marine engines, forum experience over many years consistently favours PTFE over graphite because graphite wears the shaft faster in low-speed, lightly loaded service, where PTFE's slipperiness is more useful than its chemical inertness [S3][S6].
Where Graphite Packing Wins, and Where It Fails
Graphite packing owns the high-temperature, high-speed, and steam-dominant envelope. It is widely used in chemical processing, oil and gas, power generation (steam turbines, boiler-feed pumps), pulp and paper, mining, nuclear, marine and dredging, and equipment-OEM pump and valve builds [S1][S2]. Because it is inherently self-lubricating and tolerates dry or low-flush conditions, it is also the cleaner answer in services where a flush water supply is undesirable, such as product-side agitators in chemical reactors.
The known limits are about environment, not temperature. In air or oxygen at elevated temperature, graphite oxidises, so upper temperature in oxygen-bearing atmospheres is lower than the headline +850 °F number suggests [S4]. In shaft seals on water pumps and stern gear, properly settled graphite runs well, so the wear complaints seen with graphite in governor glands do not carry over to higher-speed rotary seals [S6]. Plain graphite also tends to leave black smears, which is the reason most food, pharmaceutical, and white-mineral-oil services migrate to PTFE or to graphite yarns coated in PTFE [S2][S4].
Decision Map: Picking by Service, Not by Habit
The cleanest way to pick between PTFE and graphite braided packing is to walk four questions in order. First, what is the media? If it is a strong acid, solvent, oxidiser, or a food/pharma fluid, default to PTFE or PTFE-impregnated construction; if it is steam, hot hydrocarbon, or hot oil, default to flexible graphite [S1][S2][S4]. Second, what is the continuous temperature? Anything continuously above ~500 °F (260 °C) is graphite territory [S1].
Third, what is the shaft speed and PV? Pumps above ~1,200 fpm, or any high-PV duty, normally need graphite because PTFE will heat-soak and may carbonise at the rubbing face [S1][S4]. Fourth, is the service dry, wet, or steam? Dry or low-flush duties favour self-lubricating graphite; wet, well-flushed duties with moderate temperature can take either material. For a high-pressure gas block-valve trim problem where downstream fugitive-emissions compliance matters, the same logic shows up in ball valve datasheet parameters for high-pressure gas service, where stem-packing material, temperature, and cycle life are all decided on the same four questions.
For hybrid cases, the practical answer is a composite: PTFE/graphite braided packings with an aramid core, such as GTeek's PTFE-graphited aramid-core construction, deliver chemical resistance from the jacket, structural resilience from the aramid, and lower gland wear during break-in, with less gland modification at install [S5]. For valve-stem indication in hazardous areas where the gland has to live next to a cable gland entry on an Ex d enclosure, the same selection logic applies, and it is worth cross-checking against the spec map in ATEX Ex d IIC dry contact limit switch box spec for hazardous-area valve indication.
Trackable Signals and Next Nodes to Watch
Two engineering signals are worth tracking on real glands after install. First, monitor stuffing-box temperature rise against the manufacturer's published limit: any PTFE gland trending towards +500 °F (260 °C) is approaching its carbonisation ceiling and should be re-evaluated for flush or material change [S1]. Second, watch for colour transfer in the discharge fluid; a black tinge on a white-mineral-oil or pharmaceutical service almost always means a graphite-only packing was specified where a PTFE or PTFE-coated graphite was needed [S2][S4]. If those two signals stay clean, the packing is almost certainly the right material for the duty, and the next maintenance window should be planned against observed shaft-sleeve wear rather than against an arbitrary calendar interval.