Contact Angle
Quick answer: The contact angle is the angle where a water droplet meets the surface - higher angles give tight beading, lower angles encourage sheeting.
What it means
Contact angle describes how easily water spreads on paint. Ceramic coatings lower surface energy so water cannot wet the surface, which raises the angle and makes droplets sit taller.
Why it matters
- Explains why some coatings look beady while others are tuned for fast drying via sheeting.
- Helps set expectations for appearance, maintenance, and behaviour in hard-water or winter conditions.
Where you’ll see it
When we discuss hydrophobics, beading versus sheeting, water-spot prevention, and the visual look after washing.
Context
Car Paint Protection; Ceramic coatings
Common mistakes
- Confusing contact angle with surface tension of the liquid.
- Assuming more beading is always better - sheeting can be more practical in some conditions.
What is the difference between contact angle and surface tension?
Surface tension is like the “skin” on a liquid’s surface — it’s the force that makes water form droplets and allows small bugs to walk on it. The contact angle, on the other hand, is the angle that a drop of liquid makes where it touches a surface, which tells you how well the liquid spreads out or beads up. If the drop spreads out (low contact angle), the surface is easy to wet; if it beads up (high contact angle), the surface repels the liquid. In short, surface tension is a property of the liquid itself, while contact angle shows how that liquid interacts with a surface.
Why is it that beading is not always better than sheeting?
Beading (when water forms tight, round droplets) looks impressive and is often used to show off a coating’s hydrophobicity. However, beading isn’t always better than sheeting because it doesn’t necessarily mean the surface is cleaner or better protected. Water beads can sit on the surface longer, which means they can leave behind mineral spots or dirt when they evaporate — especially if your water isn’t pure. In contrast, sheeting happens when water quickly flows off in smooth layers, carrying away dirt and reducing the chance of water spots.
In short:
Beading = great visual, strong hydrophobic effect, but can lead to spotting.
Sheeting = less flashy, but more practical for keeping surfaces clean and spot-free.
A well-balanced coating often provides both — good beading at first, and efficient sheeting when the car is rinsed or driven in rain.
Written by Danny Argent. Last updated 04/11/2025 16:52