PTFE vs PVDF vs PFA: which fluoropolymer for chemical service?

Fluoropolymer selection starts with a bad habit: PTFE is specified because it is the material everyone knows, and the part then fails by cold flow, or cannot be welded, or costs three times what it needed to. PVDF and PFA exist precisely to cover the cases PTFE handles badly, and the decision is usually made by one property rather than by a general comparison.

Three polymers, three different compromises

PTFE is fully fluorinated, chemically inert to almost everything, and serviceable from -200 °C to 260 °C. It is also soft, creeps under sustained load, has a high coefficient of thermal expansion, and cannot be melt-processed — which means no injection moulding, no extrusion of complex profiles, and welding that is really sintering.

PVDF is partially fluorinated. It gives up roughly 100 °C of upper service temperature and some chemical breadth — strong bases, ketones and esters attack it — in exchange for strength, stiffness, creep resistance and, crucially, melt processability. PVDF sheet can be butt-welded, hot-gas welded and thermoformed into tanks and ductwork, and it holds a machined tolerance far better than PTFE.

PFA is a fully fluorinated copolymer with PTFE’s chemical and temperature performance but a melt-processable backbone. It welds, it can be lined and moulded, and its extractables are low enough for semiconductor and pharmaceutical service. It is the most expensive of the three.

Side-by-side

Creep is the property that breaks parts

A PTFE gasket, bush or valve seat under a bolted preload will relax. The material does not fail in the dramatic sense — it simply flows away from the load, the joint loses its preload, and the leak starts. Filled grades (25 % glass, 15 % graphite, 10 % carbon) slow this down considerably and are the standard fix. PVDF under the same load barely moves, which is why PVDF is the default for structural parts in a chemical line — pipe supports, valve bodies, pump components.

When weldability decides the project

If the job is a tank, a duct, a scrubber or a lining, PTFE is the wrong starting point. It cannot be welded in the field in any practical sense; it is either lined as a loose sheet or sintered in an oven. PVDF and PFA weld with hot gas or IR, produce a homogeneous joint, and can be fabricated on site. That single constraint decides most chemical-plant work before any property table is opened.

Purity, extractables and the semiconductor case

Ultra-pure water, aggressive acids at temperature and wafer contact all push toward PFA. Its surface finish after moulding is smoother than machined PTFE, it releases fewer extractables, and it resists the fluorine chemistry used in cleaning. PTFE is acceptable where the part is not in contact with the product or where extractables are not specified. PVDF sits below both and is common in general chemical and food service, not in front-end semiconductor.

Machining notes that matter

PTFE machines like soft wax: sharp, high-rake tooling, light cuts, and support right up to the cut or the part deforms. Holding a tolerance on a thin PTFE wall is genuinely hard and often requires a fixture rather than a better machine. PVDF machines like a stiff engineering plastic and holds tolerance well. PFA is soft and notch sensitive — it machines more like PTFE than like PVDF, and stressed areas will show it.

Selection rules

• Above 150 °C with chemical exposure and no structural load: PTFE.
• Any fabricated assembly that must be welded, or a part that must hold a preload: PVDF, if the chemistry allows.
• Above 150 °C and weldable, or semiconductor-grade purity: PFA.
• Tight tolerance on a thin wall: PVDF first, PFA second, PTFE only with a fixture.

Questions we are asked most

Can PVDF replace PTFE in a caustic line?

Carefully. PVDF is attacked by strong bases, particularly at temperature and under stress. For sodium hydroxide above about 10 % and 60 °C, PTFE or PFA is the safer choice.

Is virgin PTFE better than reprocessed?

For sealing and food contact, yes — reprocessed grades carry more voids and more variability. For jigs and guides, reprocessed sheet is a legitimate cost saving.

Why did my PTFE bush go oval?

Cold flow under load, almost always. A filled grade, a larger wall section or a change to PVDF solves it; a tighter tolerance does not.