Hydrophobic vs hydrophilic
Quick answer: Hydrophobic surfaces repel water (≥ 90° contact angle) so you see beading; hydrophilic surfaces (< 90°) make water spread. On cars, cured ceramic coatings are hydrophobic. “Sheeting-style” rinse-off is a hydrophobic behaviour (low hysteresis and/or high flow), not evidence of a hydrophilic coating.
What it means
These terms describe how water behaves on a surface. Hydrophobic means “water-fearing” and produces tight droplets; hydrophilic means “water-loving” and produces a continuous film. The behaviour is governed by surface energy and measured as a contact angle: hydrophobic is typically ≥ 90°, hydrophilic is < 90°.
Why it matters
- Appearance & maintenance: Hydrophobic coatings give the beady look; some are tuned for fast sheeting while still being hydrophobic.
- Water spot risk: Beads can leave rings as they dry; faster sheeting can reduce spotting in hard-water/hot conditions.
- Drying method: Beading works well with blowers/towels; sheeting-style hydrophobicity often leaves less water to remove.
Where you’ll see it
Coating descriptions, PPF top-coats, glass sealants, wash routines and aftercare advice for ceramic coatings and paint protection.
Context
Car Paint Protection; Ceramic coatings
Common mistakes
- Saying “hydrophilic coatings are better for cars” – true hydrophilic films are for anti-fog/self-cleaning glass, not for painted panels.
- Using “hydrophilic” to mean “less beady.” In our trade that usually describes a hydrophobic surface with low hysteresis or a heavy-flow rinse.
- Assuming “less beading = coating failed.” Surfactants and grime can mask beading; a decontamination often restores the behaviour.
- Confusing water’s surface tension with the surface’s surface energy.
Note on “hydrophilic sheeting” confusion: In car care, “hydrophilic sheeting” is mostly a mix-up in terms. The dramatic sheeting seen in demos is a hydrophobic surface doing its job, typically with low contact-angle hysteresis and a heavy rinse that makes droplets coalesce and run off in sheets. True hydrophilic films make water spread and cling as a continuous film, which is why they’re used for anti-fog glass, not painted panels. Some coating liquids wet easily during application, so they may behave hydrophilically when wet, but once cured the film lowers surface energy and is hydrophobic. Contamination and surfactants can also mute beading temporarily and be mistaken for hydrophilicity. A surface cannot be hydrophilic and hydrophobic at the same time in the same state.
Written by Danny Argent. Last updated 06/11/2025 14:47