What is Parylene Dimer?
The precursor that becomes a pinhole-free Parylene coating
Parylene dimer is the purified solid precursor that powers the Parylene coating process. Under vacuum, you sublime the dimer, crack it to reactive monomer, and then polymerise it on every exposed surface. The result is an ultra-thin, conformal film. In this guide, you’ll find the definition, the core chemistry, why purity matters, the main types, and simple storage tips.
Further reading: Wikipedia – Parylene
Definition
Parylene dimer (di-para-xylylene) is the starting material for Parylene coatings. It appears as a white, crystalline powder or flake. First, load the dimer into the deposition system’s dimer chamber. Next, heat it under vacuum so it goes straight from solid to vapour (sublimation). Then, split the vapour into reactive monomers and deposit them on the substrate. Finally, the monomers join to form a uniform, pinhole-free coating.
Dimer → Monomer → Polymer
At a high level, the chemistry follows three clear steps:
- Sublimation: Heat the solid dimer under vacuum to create vapour.
- Pyrolysis: Pass the vapour through a hot furnace (around 680 °C) to split it into reactive monomers.
- Polymerisation: Let the monomers enter the cool coating chamber, where they spontaneously polymerise on all exposed surfaces.
Because polymerisation happens at room temperature, the coating forms evenly over complex 3D shapes, internal voids, and sharp edges. In contrast, liquid coatings struggle with these geometries.
Purity & Quality
Dimer purity drives the final film’s appearance, dielectric strength, and deposition rate. Moisture, oxidation products, or residual catalysts can trigger discolouration, low yield, or film defects. Therefore, choose high-purity dimers (≥99.5%) for critical electronics or medical work. In addition, store the dimer in clean, airtight containers, away from heat and UV light, to preserve stability.
Find out more about our range of high purity dimers that we supply and use in our own Parylene Coating Services.
Types of Parylene Dimer (N, C, D, F)
Choose the dimer to match your environment and performance targets:
- Parylene N – Base polymer with excellent dielectric strength and deep feature penetration.
- Parylene C – Most common; strong moisture and chemical barrier with balanced properties.
- Parylene D – Higher temperature endurance with moisture protection similar to C.
- Parylene F (AF-4) – Fluorinated for extreme chemical resistance and high-frequency electronics.
In short, define the use case first, confirm substrate compatibility, and then select the grade that meets electrical, chemical, and thermal needs.
Handling & Storage
Handle Parylene dimer with clean gloves to prevent contamination. Store it in a dry area, ideally below 30 °C. Keep containers sealed until use to avoid moisture pick-up, which can cause yellowing or outgassing during deposition. With proper storage, most dimers offer a shelf life of more than two years.
Explore More on Parylene Dimers
Next steps:
Parylene Dimers Hub ·
Parylene Dimer Comparison (N, C, D, F) ·
How Dimer Purity Affects Coating Quality ·
Choosing the Right Dimer
Useful Links
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