Hydrophilic and hydrophobic surfaces: how they work and where they are used in cars

Car owners often come across the terms "hydrophilic" and "hydrophobic surface", especially when it comes to protecting the body, glass or interior. These concepts describe how a material interacts with water - attracting it or repelling it. Not only the appearance of the machine, but also its durability depends on the correct choice of coating: for example, hydrophobic compounds prevent corrosion and hydrophilic improve visibility in rain.

However, not everyone understands in what cases it is necessary to use one or another type of coating. For example, a hydrophobic layer is optimal for a windshield, which repels drops and improves visibility, and for climate control systems (for example, an air conditioner condenser), hydrophilic coatings are sometimes used so that water spreads and evaporates evenly. In this article we will analyze the physics of processes, the pros and cons of each type, as well as real tests proving that combining both properties in one product (for example, in modern ceramic coatings) gives a better result than using only one.

In order not to make a mistake with your choice, it is important to take into account not only the marketing promises of manufacturers, but also chemical composition coatings, their durability and compatibility with the materials of your car. For example, cheap hydrophobic silicone-based sprays can damage rubber seals, and some hydrophilic coatings require special surface preparation.

What is a hydrophilic surface and how does it work?

Hydrophilic surface (from Greek hydor - water and philia - love) is the material that attracts water molecules, causing them to spread out in a thin layer instead of forming droplets. This effect is achieved due to polar chemical groups on the surface that interact with water through hydrogen bonds.

In the automotive industry, hydrophilic coatings are used less frequently than hydrophobic ones, but they are irreplaceable in some cases:

• 💧 Windshields with hydrophilic layer (for example, technology Hydrophilic Coating from PPG Industries): water spreads evenly without forming droplets, which improves visibility in the rain without using wipers.
• 🌬️ Air conditioning systems: The hydrophilic coating on the evaporator prevents the formation of condensation in the form of large droplets that can flow into the cabin.
• 🔋 Batteries: some modern batteries have hydrophilic membranes for uniform distribution of electrolyte.

However, hydrophilic surfaces also have disadvantages. For example, on a car body such a coating will be accelerate corrosion, since the water does not roll off, but remains on the metal, promoting oxidation. Therefore, hydrophilic compounds are almost never used for external protection of a car - only for glass or internal parts.

⚠️ Attention: Hydrophilic glass coatings require regular updating (every 6–12 months), as their effectiveness is reduced due to contamination and mechanical wear. Do not confuse them with hydrophobic ones - the first spread water, second push away.

Hydrophobic surface: operating principle and advantages

Hydrophobic surface (from Greek phobos - fear) is the material that repels water, causing it to collect in drops and roll off. The effect is achieved due to microscopic texture or chemical composition (for example, silicones, fluoropolymers, ceramic nanoparticles). The contact angle for such surfaces exceeds 90°, and for superhydrophobic ones (for example, lotus effect) - up to 160°.

In cars, hydrophobic coatings are used everywhere:

• 🚗 Body: ceramic coatings (Ceramic Pro, Gyeon) protect paintwork from dirt, salt and UV rays, and water simply rolls off without leaving streaks.
• 🪟 Glass: hydrophobic sprays (Rain-X, AquaPel) improve visibility in the rain and reduce the frequency of using windshield wipers.
• 🔑 Door locks and hinges: treatment with hydrophobic lubricants (WD-40 Specialist) prevents freezing in winter.
• 🛞 Wheels and tires: Graphite or Teflon based coatings make it easier to clean off dirt and snow.

The main advantage of hydrophobic coatings is durability. For example, professional ceramics last 2–5 years, and high-quality glass sprays last up to a year. However, there are also nuances:

• ❌ Not all hydrophobic compounds are compatible with plastic or rubber (may cause cracking).
• ❌ Cheap products often contain silicones, which attract dust and require frequent updating.

Comparison of hydrophilic and hydrophobic coatings: table

To make it easier to choose the appropriate type of protection, let’s compare their key characteristics:

The table shows that hydrophobic coatings are more universal, but hydrophilic coatings are indispensable for specific tasks (for example, for glass in conditions of heavy rain or fog).

Where are both types of coatings used in a car?

Modern cars often combine hydrophilic and hydrophobic technologies for maximum efficiency. Here are some examples:

1. Windshield:

• 🌧️ Hydrophilic layer (inner side): prevents fogging by distributing condensation evenly.
• 🚿 Hydrophobic layer (outside): repels rain and dirt for improved visibility.

2. Body:

• 🛡️ Hydrophobic ceramics: Basic protection against corrosion and UV rays.
• 🧽 Hydrophilic detergents: used to prepare the surface before applying ceramics (e.g. CarPro Reset removes silicones and fats).

3. Ventilation system:

• 💨 Hydrophilic filter: captures moisture from the air, preventing glass fogging.
• ❄️ Hydrophobic treatment of air ducts: Prevents icing in winter.

How to properly apply hydrophobic coatings to a car

In order for a hydrophobic coating (wax, ceramic, spray) to work effectively, you must follow the application technology. Errors at this stage lead to stains, short service life or even damage to the paintwork.

Step-by-step instructions for ceramic coating:

Wash the car thoroughly with a two-phase shampoo (e.g. Koch Chemie Green Star)

Remove iron-containing particles with a decontaminant (CarPro Iron X)

Polish the surface to remove micro-scratches (abrasive paste 3M Perfect-It)

Degrease the surface with isopropyl alcohol (70% or higher)

Apply ceramics in a room with a temperature of 18–25°C and humidity up to 60%

Allow the coating to cure for 12–24 hours (do not wash the car during this time) -->

For hydrophobic sprays (for example, for glass) the process is simpler, but also requires care:

1. Clean the glass with glass cleaner (Invisible Glass).
2. Apply the spray evenly and immediately remove excess with microfiber.
3. Do not use wipers within 12 hours after treatment.

⚠️ Attention: Never apply hydrophobic coatings to hot surfaces (for example, immediately after washing in the sun). This will lead to uneven drying and staining. The optimal body temperature is 15–25°C.

Myths and misconceptions about hydrophilic and hydrophobic coatings

The auto chemical market is full of myths that interfere with the right choice. Let's look at the most common ones:

Myth 1: “The hydrophobic coating makes the car completely invulnerable to dirt.”

❌ Reality: Hydrophobic compounds make cleaning easier, but do not eliminate it. Dirt, tar and bird droppings still stick, especially if the coating has not been renewed for a long time. For example, ceramics Ceramic Pro 9H protects against chemical damage, but not against mechanical damage (scratches from branches).

Myth 2: “Hydrophilic glass does not need wipers.”

❌ Reality: The hydrophilic coating improves visibility in light rain, but wipers are still necessary in heavy rain or snow. Technology Hydrophilic Coating from PPG reduces the need for their use by 30–40%, but not by 100%.

Myth 3: “All hydrophobic sprays are the same.”

❌ Reality: The compositions are very different:

• 🧪 Silicone (cheap): short-term effect (1–3 months), attract dust.
• 💎 Fluoropolymer (mid price segment): lasts 6–12 months, resistant to detergents.
• 🧂 Ceramic (premium): service life 2–5 years, high scratch resistance.

Myth 4: “Hydrophilic coatings harm the body.”

❌ Reality: It is not the coating itself that causes damage, but its misuse. For example, if a hydrophilic compound is applied to uncleaned metal, it will accelerate corrosion. But it is absolutely safe on glass or plastic parts of the interior.

FAQ: Frequently asked questions about hydrophilic and hydrophobic coatings

1. 70% isopropyl alcohol - 50 ml
2. Polydimethylsiloxane (silicone oil) - 10 ml
3. Distilled water - 40 ml