F1 Explained: What is flow vis paint and why is it used?

The 2025 Formula 1 season has officially arrived, with three days of pre-season testing in Bahrain having kicked off this morning.

Teams and drivers will now put their cars through their paces at Bahrain International Circuit before heading to Melbourne, Australia, for the season opener in mid-March.

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However, if you are tuning into the action this morning, you may notice some cars covered in fluorescent yellow or green paint.

These aren't artistic flourishes though; they hold the key to unlocking performance secrets. This mysterious paint, called flow-vis, plays a crucial role in pre-season testing, offering valuable insights into a car's aerodynamic performance.

But what exactly is flow-vis and why is it so crucial? Let's find out.

What is the neon paint on F1 cars in testing?

Flow-vis, short for flow visualization, is more than just paint; it's a window into the invisible forces shaping a car's behavior on the track. This special blend, made of fluorescent powder mixed with light oil, usually paraffin oil, acts as a temporary sensor.

Engineers apply the paint to specific parts of the car that they want to investigate. While the paint is still wet, the car is driven out of the pit area and onto the circuit. As the car speeds up and takes corners, the airflow interacts with the paint and causes it to streak and dry in unique patterns.

These patterns act as a visual map, revealing crucial information about how air flows over the car's surface and highlighting areas of separation, turbulence, and efficiency.

After the car is returned to the garage, engineers take photographs and begin to examine the painted areas. This data is gold dust for them, as it provides insight into how the flow interacts with crucial components like the wings, diffuser, and underfloor of the car. It also confirms the results seen in CFD (computational fluid dynamics) or wind tunnel testing.

Using this data, engineers can make targeted adjustments, such as fine-tuning wing angles, modifying bodywork elements, or experimenting with different configurations.

Engineer Rob Smedley, who previously worked for Ferrari and Williams, explains how flow-vis works:

"You paint it liberally on the car, the car then goes out and as it’s moving up to speed and going through a cornering condition, the paint dries as the light oil evaporates and you end up being able to visualize, very clearly, what sort of flow structures you've got.

"When we then analyze that – we’re usually looking for things like separation, as in where the flow's separating and we’re not getting decent flow structures across the surfaces of the car. That can then tell the aerodynamicists a lot about what's going on upstream of that, and hopefully, that helps them to rectify certain problems on the car."

READ MORE: F1 2025 Testing: When are Lewis Hamilton, Max Verstappen and others driving in Bahrain?

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