Ahead of today's opening session the air temperature is 25 degrees C, while the track temperature is 42 degrees. It is bright but cloudy. Indeed, there is a 30% chance of rain.

This week's upgrades are a new Floor Edge and Diffuser for Red Bull, Rear Wing, Coke/Engine Cover and Floor Body / Edge for Ferrari and Sidepod Inlet and Diffuser at Mercedes.

McLaren has a new Front Corner and Aston Martin a new Front Wing, Front Wing Endplate, Nose, Rear Wing Endplate and Beam Wing, while AlphaTauri has a new Rear Wing and Rear Wing Endplate and Williams a new Front Wing and Coke/Engine Cover.

There are no new components for Alpine, Alfa Romeo or Haas.

Unlike Monaco, Barcelona will be the perfect proving ground for upgrades, not only this week's but those first run at the Principality, indeed, teams like Mercedes are either going to leave here a lot happier or sincerely worried.

At Ferrari, which has followed Mercedes example and introduced new sidepods, it is understood the team will be running the old layout and the new for comparison purposes.

In this session, and again in FP2, the drivers will try out two additional sets of hard tyres that feature the new construction that will be used from the British Grand Prix onwards. Apart from the use of some new material, which has already been homologated following an extensive test programme, the latest specification is identical to the previous version. Initially this was scheduled for 2024, but its introduction has now been brought forward to make the structure more resistant to fatigue, as the loads generated by the current cars have already reached the targets set for the end of the season after only a few races. This new construction has no impact though on the technical parameters or performance of the tyres.

The lights go green and local hero Alonso leads the way, followed by Stroll, de Vries, Sainz and Bottas. As more drivers head out, most are running the prototype hard tyre.

Of course, with all those updates to try there are some who want to get to work on 'regular' tyres, among them Russell, Hamilton and Norris.

Upgrades also mean lots of flo-vis and aero rakes.

Of the first wave, Perez goes quickest with an 18.781, only to be leapfrogged by his Red Bull teammate who stops the clock at 17.425.

A 17.800 sees Tsunoda go second, ahead of Ocon, Gasly, Hamilton and Hulkenberg, though all are demoted when Perez improves to 17.465, just 0.040s off his teammate's pace.

At which point Verstappen raises the bar with a 16.583. Both the Bulls are on mediums.

"A bit of bouncing on the entry at the last corner," reports Russell. He also says that his steering feels light.

Having started the session on softs, Hulkenberg fits another set of the red-banded tyres.

Perez posts a 16.420 but again his teammate goes quicker (15.945), as Sainz goes ninth and Leclerc 12th.

Hulkenberg (softs) improves to third with a 17.436.

"I'm starting to bounce as I go into the final corner," reports Perez, echoing Russell's earlier complaint.

In fifth, Ocon is the fastest of the prototype runners as more drivers switch to the mediums.

Albon (proto) improves to eighth with a 17.853.

On the mediums, Sainz improves to third with a 17.085, the Spaniard's car fitted with the upgrades while Leclerc has the old components. Moments later, Sargent (mediums) goes fourth with a 17.086.

Now Verstappen complains of bouncing, in Turn 10 and the final corner.

A 16.363 sees Gasly (mediums) go second, while Alonso goes fourth with a 16.876.

De Vries improves to fifth with a 17.003 as Perez heads out on softs. Moments later, Verstappen following his teammate, the world champion also sporting the red-banded rubber.

"Some porpoising into the last corner," reports Norris, the 'P word' returning to the F1 vocabulary.

Oh dear, on the softs, Verstappen posts a 14.606. His teammate can only manage a 15.374.

On the softs, Magnussen goes third with a 16.321, while Hulkenberg, on fresh softs, goes sixth (16.536). Thus far, only Haas and Red Bull have tried the red-banded rubber.

Hamilton and Russell, currently 18th and 19th, head out on the prototype tyres.

Switching to softs, Zhou goes third (15.906) and teammate Bottas fourth (15.978) as more drivers make the switch.

Ocon pits after reporting seeing pieces of carbon fibre fall from his car after running wide over the kerb.

A 15.726 sees a soft-shod Sainz go third, ahead of Norris, Zhou and Bottas.

With 15 minutes remaining, though at the other end of the timesheets, the Mercedes pair have completed the most laps - 23 apiece - as they continue to acquire data, albeit all their running on the prototype rubber.

Running the older-spec Ferrari, Leclerc goes third (15.694), marginally up on his teammate.

The Monegasque is subsequently demoted when de Vries posts a 15.504.

With 10 minutes remaining, Russell bolts on a set of softs. He subsequently posts a 15.753 to go eighth.

Alonso improves to 8th with a 15.727 as Hamilton heads out on softs. The seven-time champion posts a 15.845 to go 12th.

Gasly improves to fifth with a 15.545 as a 15.689 sees Magnussen claim a late 6th.

A brief wobble for Gasly in Turn 1, as Alonso improves to sixth with a 15.547.

"Me and Gasly touched, reports Sargeant as the Alpine driver has another moment.

The session ends. Verstappen is quickest, ahead of Perez, Ocon, de Vries, Gasly, Alonso, Magnussen, Leclerc, Sainz and Russell.

Norris is eleventh, ahead of Hamilton, Zhou, Tsunoda, Stroll, Bottas, Piastri, Hulkenberg, Sargeant and Albon.

Check out our Friday gallery from Barcelona here.