Parylene Dimer Comparison (N, C, D & AF-4)

Parylene dimers form the foundation of every Parylene coating, but each type—N, C, D, and the fluorinated “F” family—offers distinct performance characteristics.

In industry, “Parylene F” is often used as a shorthand for fluorinated parylenes, most commonly discussed as VT4 and AF-4 variants (supplier naming can vary, and AF-4 is frequently marketed as Parylene HT). Selecting the right dimer affects not only coating thickness and adhesion strategy, but also moisture resistance, dielectric behaviour, and temperature capability.

This guide compares the main Parylene dimers side by side and clarifies the AF-4 vs “F” naming, so you can choose the best match for your application.

Overview

Although all Parylene coatings share the same deposition principle—sublimation, pyrolysis, and polymerisation—the chemical substitution on the dimer molecule strongly influences electrical behaviour, barrier performance, thermal stability and surface energy.
In practice:

• Parylene N – Base polymer (no halogen). Often chosen for excellent dielectric behaviour and good penetration into fine geometry.
• Parylene C – Monochloro-substituted. Widely used for balanced general protection, including strong moisture/ionic barrier performance.
• Parylene D – Dichloro-substituted. Selected when you need higher temperature stability than C while retaining good barrier behaviour.
• Fluorinated “F” family – Typically discussed as VT4 and AF-4 (often marketed as Parylene HT). Fluorinated grades are used for higher thermal/oxidative stability, lower dielectric constant and lower surface energy (which can reduce adhesion unless the right surface prep/adhesion promotion is used).

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Chemical Structure Differences

The key distinction between each dimer lies in its substitution (chlorine or fluorine) and where those atoms sit in the molecule. This changes crystallinity, chain mobility and surface energy.

Important: “Parylene F” is commonly used as a family label for fluorinated parylenes. AF-4 is a key member of that family, but “F” is not always synonymous with AF-4 in supplier literature.

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Performance Comparison Table

Published property data can vary by supplier (purity, stabilisers), deposition recipe and post-bake conditions. The table below is therefore directional and intended for early selection—not as a substitute for qualification testing.

For most electronics, Parylene C remains the balanced, mainstream choice. Parylene D and the fluorinated family (VT4/AF-4) tend to appear when temperature, chemistry, UV or dielectric-constant goals push beyond standard requirements.

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Choosing the Right Dimer

When selecting a Parylene dimer, balance the functional and environmental requirements:

• Electrical Insulation: Often Parylene N for thin-build dielectric performance (confirm against your frequency range and test plan).
• Moisture / Ionic Barrier: Typically Parylene C as the general-purpose barrier workhorse.
• Higher-Temperature Operation: Commonly Parylene D, or fluorinated grades where limits are more demanding.
• Extreme Chemical / UV / Low Surface Energy: Consider fluorinated options (VT4 / AF-4), but plan adhesion strategy carefully.

If you’re writing a controlled spec, include: dimer grade naming (including supplier designation), thickness range, adhesion promotion method (if any), masking/keep-outs, acceptance criteria, and qualification tests.

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Explore More on Parylene Dimers

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Note: This article provides general technical guidance only. Final design, safety, and compliance decisions must be verified by the product manufacturer and validated against the applicable standards.