PTFE vs Polyurethane Hydraulic Seals – Which Material to Specify and When

PTFE vs Polyurethane Hydraulic Seals – Material Selection Guide

Choosing between PTFE and polyurethane for hydraulic cylinder seals is one of the most frequently asked material selection questions Kaybin receives from maintenance engineers and OEM designers across South Africa. Both materials are widely used in piston seals, rod seals, wiper seals and U-cups, but they perform very differently depending on pressure, speed, contamination exposure and the specific duty of the cylinder.

This guide explains the key differences between PTFE and polyurethane hydraulic seals, when to specify each material, and the hybrid constructions that combine the advantages of both.

Polyurethane Hydraulic Seals

Polyurethane (PU) is the dominant material for high-pressure hydraulic cylinder sealing in mobile and industrial applications. Its combination of mechanical strength, wear resistance and extrusion resistance makes it well suited to demanding hydraulic duty where single-lip seals must hold pressure, resist extrusion through clearance gaps and survive shock loading without deformation.

Key Properties of Polyurethane Seals

Polyurethane seals offer high tensile strength and tear resistance, strong extrusion resistance through small clearance gaps, excellent abrasion resistance in contaminated hydraulic systems, and good pressure capability across a broad hardness range. PU seals are commonly supplied in Shore A hardnesses from approximately 85A to 95A for standard hydraulic duties, with harder grades used where extrusion gaps are larger or where pressure spikes are frequent.

PU performs well in mineral oil hydraulic fluids and water-glycol blends commonly used in mining applications. Temperature range is typically –30°C to +100°C, with peak limits that are application-dependent. PU seals are not suitable for phosphate ester fluids, strong acids or elevated-temperature steam environments.

When to Specify Polyurethane

Specify polyurethane hydraulic seals for high-pressure cylinders where extrusion resistance is critical, mining and earthmoving hydraulic systems operating in contaminated environments, cylinders with shock loading and pressure spikes, applications where wear resistance on rod and bore surfaces must be maximised, and OEM hydraulic cylinders requiring long service life between maintenance intervals.

PTFE Hydraulic Seals

PTFE (polytetrafluoroethylene) hydraulic seals operate on fundamentally different mechanical principles to polyurethane. PTFE is a hard, dimensionally stable engineering plastic with an extremely low coefficient of friction. PTFE seals are not energised by their own elasticity — they require an energiser element (typically an O-ring or elastomeric spring) to generate the sealing force against the rod or bore surface.

Key Properties of PTFE Seals

PTFE seals deliver very low friction and minimal stick-slip behaviour, outstanding chemical resistance across a broad range of aggressive fluids, excellent performance at elevated temperatures well beyond polyurethane limits, dimensional stability and resistance to compression set, and compatibility with phosphate ester, water-based and aggressive chemical fluids. The low friction of PTFE makes it the preferred material where smooth, consistent rod extension and retraction are critical, such as precision machine tools, metering cylinders and servo-controlled systems.

Filled PTFE Grades

Virgin PTFE has relatively low mechanical strength and wears more quickly under dynamic loading. Filled PTFE grades — incorporating carbon, graphite, glass fibre, bronze or other fillers — significantly improve wear resistance, load capacity and creep resistance. The correct filler type is selected based on the specific duty conditions, particularly the surface material of the rod or bore the seal contacts.

When to Specify PTFE

Specify PTFE hydraulic seals for cylinders requiring low friction and smooth controlled movement, systems using phosphate ester or aggressive hydraulic fluids, high-temperature environments beyond the capability of polyurethane, applications requiring chemical resistance such as chemical processing or food-grade hydraulic systems, and servo-hydraulic and proportional control systems where stick-slip causes positioning error.

PTFE-Polyurethane Hybrid Seals

The most common high-performance hydraulic seal construction combines the advantages of both materials in a single seal assembly. A PTFE primary sealing element — which contacts the rod or bore — is energised by a polyurethane or elastomeric O-ring spring element. This construction delivers the low friction and chemical resistance of PTFE at the sealing interface, backed by the elastic recovery and sealing force of the energiser element.

Composite seals of this type are widely used in precision hydraulic cylinders, servo systems, food-grade applications and any duty where reducing stick-slip or extending fluid compatibility is important without sacrificing reliable sealing performance.

Direct Comparison Summary

Polyurethane seals are the better choice where high extrusion resistance is needed, where shock loading and abrasive contamination are present, and where mineral oil or water-glycol fluid is used. PTFE seals are the better choice where low friction and smooth movement are critical, where chemical resistance beyond polyurethane limits is required, and where elevated temperatures or aggressive fluids exclude elastomeric options. Hybrid PTFE-energised seals combine the benefits of both and are often the optimum specification for precision and chemically demanding hydraulic applications.

Hydraulic Seal Selection Support — Kaybin

Kaybin manufactures hydraulic cylinder seals in polyurethane, filled PTFE and composite constructions for industrial, mining, mobile and OEM hydraulic applications across South Africa and Africa. Seals are manufactured to groove dimensions, pressure class and fluid specification. To confirm the correct material and seal profile for your application, provide your bore and rod diameter, groove dimensions, working pressure, fluid type and operating temperature and Kaybin will specify and manufacture the correct hydraulic seal to duty.