Fillers - Diffusers

Fillers and diffusers are added to some waxes and sealants to hide imperfections in the paintwork.

Most cars will get wash marks, which are very fine scratches in the paintwork which can be seen under harsh sunlight and make the car look aged.

Our aim in polishing a car is to remove these micro-scratches, but the alternative offered by manufacturers of retail car care products is to hide them with fillers and diffusers. Very few products will explicitly say this is what they are doing, but any product marketed for dark coloured cars or for black cars is almost certainly doing just that.

Fillers are to fill scratches and can completely hide micro-maring, and diffusers are often ceramic nano-beads which are there to diffuse and scatter light, which makes the light reflected by harsh scratches less harsh.

These products can be very useful and fairly effective at hiding imperfections on dark coloured cars. However, they can cause problems, as they hide buffer trails and holograms which may then be later revealed when these products, which are temporary, are burned off by the sun and worn away by the elements.

What it means

Fillers and diffusers are the parts of a polish or glaze that make defects look smaller or disappear without actually cutting the paint flat. Fillers are resins, waxes and other solids that sit in fine scratches and low spots, levelling them just enough to improve reflections. Diffusers are oils and other components that change the way light bounces off the surface, softening the appearance of remaining marks. Together they can make swirl marks, wash-marks and light haze far less obvious, at least for a while.

Why it matters

• Explains “instant transformations”: Many rapid valeting and trade products rely heavily on fillers and diffusers to make tired paint look glossy in a short time.
• Difference between real and cosmetic correction: With fillers and diffusers, the car can look corrected when in reality the scratches are still there under a thin cosmetic layer.
• Results may fade: As products weather or are stripped with panel wipe, the effect reduces and the true condition of the paintwork reappears.
• A useful tool when used honestly: On thin, old or delicate paint, fillers and diffusers can be the safest way to improve appearance without aggressive cutting.

Where you’ll see it

You will see fillers and diffusers mentioned in discussions about chemical polishes, glazes and some all-in-one products. Detailers and inspectors may talk about heavy use of fillers, defects returned after removing fillers or retail polishes with lots of diffusing oils. It is a common topic when explaining why a freshly valeted auction car can look dramatically worse a few washes later.

Context

Fillers and diffusers belong to the “cosmetic improvement” side of polishing. Corrective compounds use abrasives to physically level the clearcoat, permanently reducing defects within the limits of safe paint thickness. Chemical polishes and glazes often add fillers and diffusers to boost gloss and mask the remaining fine marks. Professional correction work usually avoids relying on heavy filling when a long term result is required, instead using panel wipe and inspection lights to confirm that defects are genuinely removed before applying protection. For budget work, older cars or dead paint, controlled use of fillers and diffusers can still be the most sensible compromise.

Common mistakes

• Assuming that because paint looks good straight after polishing, all defects have been permanently removed instead of largely hidden.
• Applying ceramic coatings or long term sealants over fresh fillers and diffusers without proper panel wipe, which can weaken bonding.
• Using heavy filling to disguise failing clearcoat or serious defects that really need repair and repaint.
• Judging a car only under soft lighting and immediately after a filled glaze, then being surprised when the true condition shows up in sun or after a few strong washes.

Written by Danny Argent. Last updated 21/11/2025 16:42