The Short Answer

If you need the best all-around performer: choose PVDF. If you need maximum chemical or thermal resistance: choose PTFE. If your application is general-purpose and cost is a factor: choose Polypropylene.

But the full picture is more nuanced — and getting it right matters. Read on for a detailed breakdown.

Understanding the Three Materials

PVDF — Polyvinylidene Fluoride

PVDF is a semi-crystalline fluoropolymer that sits at the intersection of performance and practicality. It offers exceptional chemical resistance, high mechanical strength, and excellent dimensional stability — all in a material that machines cleanly to tight tolerances.

Why engineers choose PVDF:

• Resists virtually all acids, halogens, and aqueous chemical environments
• Maintains strength and stiffness under compressive bolt loads (critical for flange joint integrity)
• Operating temperature up to 280°F (138°C)
• Outstanding resistance to UV degradation — suitable for outdoor piping
• Low moisture absorption ensures dimensional stability over time
• Available in high-purity grades for semiconductor and pharmaceutical applications

Where PVDF has limitations: it is not ideal for strong ketones, esters, or certain amines. At temperatures exceeding its rated limit, chemical resistance degrades rapidly. It is currently the highest-cost option among the three materials — supply chain disruptions during COVID made PVDF significantly harder to source, driving prices up above PTFE, where they have remained.

PTFE — Polytetrafluoroethylene

PTFE is the gold standard for chemical resistance in industrial thermoplastics. Its carbon-fluorine backbone is one of the strongest bonds in chemistry, giving PTFE an almost universal resistance profile. There is virtually no industrial chemical that will attack PTFE under normal operating conditions.

Why engineers choose PTFE:

• Inert to virtually all chemicals, including fuming acids, strong bases, and organic solvents
• Highest operating temperature of any common thermoplastic: up to 500°F (260°C)
• Excellent performance in steam and high-temperature corrosive service
• FDA and USP Class VI compliant — ideal for pharmaceutical and food processing
• Extremely low coefficient of friction — does not bond to gaskets or adjacent surfaces

Where PTFE has limitations: its mechanical weakness is the main tradeoff. PTFE is prone to cold-flow (creep) under sustained compressive stress. In flange applications where bolt torques are high or bolt loads are uneven, PTFE spacers can deform over time, potentially compromising the joint seal.

Polypropylene (PP)

Polypropylene is the most widely used thermoplastic in the world for good reason — it offers solid chemical resistance, excellent machinability, and a price point that makes it the practical choice for many general-purpose applications.

Why engineers choose Polypropylene:

• Resistant to most dilute acids, bases, and aqueous salt solutions
• Good resistance to organic solvents at ambient temperatures
• Operating temperature up to 225°F (107°C)
• Lightweight — approximately half the weight of PVDF
• Cost-effective — significantly less expensive than fluoropolymers
• Food-grade grades available for potable water and food processing

Where PP has limitations: polypropylene is not suitable for oxidizing acids (concentrated sulfuric, nitric, chromic), aromatic or chlorinated hydrocarbons, or service above its temperature limit. It has poor UV resistance in outdoor applications without UV stabilizers, and its chemical resistance degrades more rapidly with temperature than fluoropolymers.

Side-by-Side Comparison

Decision Guide: Which Material Is Right for Your Application?

Choose PVDF when:

• Your process fluid is acidic, halogenated, or chemically aggressive
• You need a material that can handle moderate-to-high temperatures
• Mechanical strength and creep resistance matter (high bolt load flanges)
• Your system is installed outdoors with UV exposure
• You need purity compliance without going to full PTFE cost

Choose PTFE when:

• You have the most aggressive chemical environment — fuming acids, strong oxidizers, concentrated solvents
• Operating temperatures exceed 280°F or the system sees steam
• The application requires pharmaceutical-grade purity (USP Class VI)
• Non-stick, low-friction surface contact is important
• Long service life in the harshest possible conditions is the priority

Choose Polypropylene when:

• The process fluid is dilute acids, caustics, or aqueous solutions
• Operating temperature stays below 200°F
• Budget is a significant factor and fluoropolymer performance is not required
• The system is a general-purpose water treatment, chemical dosing, or industrial water application

A Note on Lined Pipe Flange Dimensions

All three materials are available from SG&P in configurations engineered specifically for lined pipe systems. Lined pipe flanges have different face dimensions than standard steel flanges — the liner extends to the flange face, altering the bolt circle, OD, and bore geometry.

SG&P manufactures to lined-pipe flange dimensions as standard across all 11 spacer types: Blind Ring, Standard Ring, Blind Full Face, Standard Full Face, Tapered Bore Ring, Tapered Bore Full Face, Orifice Ring, Orifice Full Face, Reducing Ring, Reducing Full Face, and Compensation Ring spacers. Every part is custom-machined to your exact specification.