Walk into any PTFE supplier's catalogue and you will see two distinct types of PTFE sheet: molded (sometimes written "moulded") and skived. They look identical to the eye — both are white, both feel the same, both have the same chemical resistance. But they are made differently, have subtly different property profiles, and are genuinely better suited to different applications. This guide breaks down every technical and practical distinction so you can make the right specification with confidence.
Manufacturing Processes — The Core Difference
Molded PTFE Sheet
Molded sheets are produced by filling PTFE powder into a flat rectangular steel die, applying high pressure with a hydraulic press (50–100 MPa), ejecting the green preform, and sintering it in an oven above 380°C. The entire thickness of the sheet is formed as a single monolithic structure. This process produces sheets up to 100 mm thick with isotropic (equal in all directions) properties throughout the cross-section.
Skived PTFE Sheet
Skived sheets start life as a large cylindrical sintered PTFE billet — effectively a very large molded rod. This billet is mounted on a lathe-like machine and rotated while a precision-ground blade peels a continuous thin sheet from the rotating outer surface — exactly like unrolling a coil of paper. This "skiving" process produces very thin, uniform-thickness sheets that cannot be made by direct moulding because it is practically impossible to press and sinter thin sections uniformly. The resulting sheet has a slight directionality along the skiving direction.
Property Comparison: Molded vs Skived
| Property | Molded Sheet | Skived Sheet |
|---|---|---|
| Minimum thickness | 3 mm (practical limit) | 0.5 mm (thinner possible in thin film) |
| Maximum thickness | 100 mm + | 6 mm (practical skiving limit) |
| Maximum sheet area | Typically 600 × 600 mm for thick sheets | Up to 1500 × 1500 mm for thin sheets |
| Thickness tolerance | ±0.3–0.5 mm | ±0.05–0.15 mm (tighter) |
| Property isotropy | Isotropic (same in all directions) | Slight anisotropy in skive direction |
| Surface finish | Good (may need facing for sealing) | Excellent — both faces very smooth |
| Density uniformity | Good for moderate thickness; may vary slightly in very thick blocks | Excellent — very uniform through thickness |
| Compressive strength | Slightly better in through-thickness direction | Equal in all orientations |
| Flexibility | Rigid above 5 mm; semi-rigid 3–5 mm | Flexible below 2 mm; semi-flexible to 6 mm |
Which to Specify for Common Applications
| Application | Best Choice | Key Reason |
|---|---|---|
| Flange gaskets (standard, 1.5–3 mm) | Skived sheet | Tighter thickness tolerance; smoother sealing surface; large sheet area for efficient nesting |
| Flange gaskets (heavy duty, 4–6 mm) | Molded sheet | Better compressive strength; less cold flow at higher bolt loads |
| Tank and vessel lining (bonded) | Skived sheet (2–4 mm) | Thin, flexible; conforms to vessel curvature; large sheet area reduces joints |
| Machined flat components (slide pads, bearing pads) | Molded sheet | Isotropic properties; sufficient thickness for facing and profiling |
| Laboratory bench cover | Skived sheet (3–6 mm) | Large, flat sheets; smooth surface; uniform thickness |
| Electrical insulation panels | Either — depends on required thickness | Both give excellent dielectric properties |
| Thick machined blocks / blanks | Molded sheet / billet | Only molded process can produce sufficient thickness |
| Thin diaphragms and membranes | Skived sheet (0.5–2 mm) | Consistent thin section with good flexibility and burst strength |
Visual Identification
It is not easy to distinguish skived from molded sheet visually on a piece already cut to size. However, some indicators:
- Skived sheet tends to have a very smooth, almost translucent surface finish on both faces, with a characteristic slight grain in one direction if you look at an angle in good lighting
- Molded sheet may show slight roughness or a matte finish on the pressed face; the edges may show slight density variation in very thick sheets
- Any sheet below 3 mm is almost certainly skived — compression moulding cannot reliably produce sheets below 3 mm with consistent density
- Any sheet above 6 mm is certainly molded — skiving above 6 mm becomes impractical
Frequently Asked Questions
Is the chemical resistance the same for molded and skived PTFE?
Yes — the chemical resistance of PTFE is determined by the polymer chemistry, not the manufacturing method. Both molded and skived virgin PTFE offer identical chemical resistance. The process type does not change the base polymer composition or its reactivity with chemicals.
Can skived PTFE sheets be used for structural applications?
Skived sheets below 3 mm are flexible and not suitable for structural load-bearing applications. For slide bearings, bridge bearing pads, and structural components, use molded PTFE sheet in 4 mm or greater thickness, or specify the application-specific filled grade (glass or bronze filled molded sheet) for improved compressive strength and creep resistance. See our bridge bearing pads guide for structural applications.
PTFE Sheets — Molded & Skived, All Grades
Virgin, glass-filled, carbon-filled, and bronze-filled PTFE sheets. Skived from 0.5 mm; molded to 100 mm. Standard and custom sheet sizes. Cut-to-size gaskets also available.
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