Intermediate and wet tyres
When it rains, slicks stop working because water sits between the rubber and the track. Pirelli makes two treaded tyres for wet conditions: the intermediate (green sidewall) for a damp track or light rain, and the full wet (blue sidewall) for heavy rain and standing water.
Intermediates
The intermediate, nearly always called the "inter", has shallow grooves that clear a moderate amount of water. It's the tyre you'll see most often in wet sessions, because a track is more often damp or drying than truly soaked.
Inters work best on a surface that's wet but has no puddles. On a drying track they overheat and wear quickly, especially once a dry line appears. Turkey 2020 is a famous case: Lewis Hamilton kept the same set of inters for around 50 laps until they were worn almost smooth, effectively turning them into slicks on a drying track, and won the race to clinch his seventh title.
Full wets
The full wet has much deeper grooves and pushes away far more water. Pirelli says that at 300 km/h a full wet can clear around 85 litres of water per second per tyre, compared with about 30 litres for an inter.
You don't see full wets used for long very often. They're slow, and conditions bad enough to need them are usually bad enough that the spray thrown up by the cars leaves drivers unable to see. In that situation race control tends to keep the cars behind the safety car or stop the session with a red flag rather than let them race.
How many sets drivers get
Each driver has 5 sets of inters and 2 sets of full wets for the weekend. In practice sessions they can only use wet tyres once race control has declared the track wet. After that, any tyre is allowed for the rest of the session. The full table of allocations is on the tyre rules page.
Wet starts
If the race director thinks the track is too wet for a normal start, the race begins behind the safety car. In that case every driver must use full wets until the safety car comes in. After a few laps, once conditions are judged safe, the cars line up on the grid for a standing start. More on this in racing in the wet.
The crossover point
The hardest call in a wet race is when to change tyres. As rain eases and a dry line forms, there comes a point where slicks become faster than inters. That's the crossover. It happens again in reverse when rain starts to fall on a dry track.
Get it right and a driver can gain many places in a couple of laps. Go too early and they'll be sliding around on cold slicks, losing seconds a lap or crashing. Go too late and everyone who stopped earlier will have gone past. Drivers often make this call themselves because they can feel the grip changing before the data shows it.
The same choice exists between inters and full wets. Teams watch the lap times of anyone who gambles first, and once one car shows the other tyre is quicker, the rest usually follow within a lap or two.
Wet tyres and the two-compound rule
In a dry race, every driver must use two different dry compounds. If a driver uses inters or wets at any point in the race, that rule no longer applies to them. So a race that starts wet and dries out can be finished on just one type of slick.
Why wet races mix up the order
Rain shrinks the advantage of a fast car. Grip is low for everyone, so driver feel and good tyre calls matter more than downforce. Wet races are where big upsets happen. In Brazil in 2024, Max Verstappen started 17th and won in heavy rain, while drivers around him lost out to crashes and badly timed stops.