The track evolved rapidly: from a fastest time in FP1 that was slower than last year's benchmark, the quickest time overall in FP2 - by Mercedes driver Valtteri Bottas on the soft compound - was more than 1.5 seconds faster than the 2018 equivalent.
His team mate Lewis Hamilton set his fastest time of the day (second-quickest overall) on the medium tyre, which could be an interesting solution to get through Q2 tomorrow.
There's a performance gap of just over 0.6 seconds between the soft and the medium so far, with the medium and the hard separated by a similar gap (although this is difficult to assess precisely due to track evolution).
There have been a few new things to get used to: a new pit entry and some new asphalt, which looks visually different to the asphalt that's already in place.
There was some graining in FP1, with the cars sliding on the slippery surface.
The competitive order appears to be interesting, with McLaren looking strong throughout both free practice sessions.
Warm weather is set to be the case all weekend, with track temperatures peaking at 52 degrees centigrade during the afternoon.
Mario Isola: "The remarkable thing about today's session was the fact that Lewis Hamilton set his fastest time on the medium tyre, as opposed to everyone else who set their best time on the softs, as is usual for a Friday. This means that there's a strong chance of seeing these medium tyres in Q2, with some drivers perhaps using them to start the race on. There was a high degree of track evolution, with the circuit being very slippery this morning. This caused the cars to slide a lot, as a result of which we saw some graining. In warmer temperatures and with more rubber on the track, this phenomenon was progressively reduced, to the extent that the fastest FP2 time was more than 1.5 seconds quicker than last year. We anticipate seeing the lap times get even quicker tomorrow, as they have done throughout the season to date."
Check out our Friday gallery from Le Castellet, here.