Ahead of today's opening session the air temperature is 21 degrees C, while the track temperature is 27 degrees.

There are a couple of reserve drivers on duty this morning, Alfonso Celis replacing Esteban Ocon at Force India and Antonio Giovinazzi in Kevin Magnussen's Haas.

This weekend, despite the fact that it marks the last race before the summer break, sees important upgrades for both Red Bull and Sauber, both teams seeking a substantial step forward in the months ahead.

The nature of the track should suit McLaren courtesy of the low demand on the engine, while Ferrari should also benefit in terms of its tyre efficiency.

Talking of Sauber, in the moments before the start of the session the Swiss outfit confirmed a new deal with Ferrari for 2018 which will see it using current-spec power units.

The lights go green and Verstappen leads the way. The Red Bull driver is followed by Ericsson, Sainz, Giovinazzi, Wehrlein and Raikkonen.

A good mixture of mediums and supersofts while Ricciardo is on the softs.

Just 4 minutes in and all 20 drivers have been out, Ricciardo (22.421) posting the first time of the weekend. The Australian subsequently improves to 41.469, then 21.212.

Ricciardo heads back to the pits and silence falls over the track.

Back in the garage, mechanics swarm over Ricciardo's car, removing the new front wing and wiping off the flo-vis from the similarly new rear wing.

Meanwhile, Christian Horner reveals that Ricciardo has already matched his S2 time from qualifying last year.

After several minutes of total inactivity, Palmer heads out to give the crowds something to actually look at. The Briton is on the supersofts, as are Alonso and Stroll who join him.

Palmer, who is running the new floor this weekend, posts 24.416.

Vandoorne spins at T2, the rear of the car simply getting away from him, thereby bringing out the yellows. Unable to restart the car he is told to shut-down before attempting again.

As he gets going again, Grosjean spins at T9 and lightly clouts the barrier with the rear of the car. "OK, box, I hit the wall," he tells the team, "there is something wrong with the rear of the car." Well if there wasn't, there is now.

Replay shows his rear wing took the brunt of the hit.

In the meantime, Raikkonen has gone quickest (20.078), ahead of Vettel, Hamilton, Bottas, Ricciardo and Vandoorne.

Bottas improves with a 20.053 to take the top spot as Kvyat, Celis and Perez remain the only drivers still to post a time.

Vettel spins at T9, but unlike Grosjean keeps it out of the barriers.

Perez is warned of a headwind in T1 and T5. Moments later the Mexican runs wide at T11.

Another off for Haas, but this time it's Giovinazzi who is in the barriers at T11 and has caused quite some damage to the car, especially the front left-hand corner.

The session is Red Flagged as the Haas is removed.

Asked if he is OK, the Italian sighs: "yeh!" Replay shows the Italian lost the car mid-corner.

With hardly any use throughout the year the circuit is always dusty, the situation not helped by the strong headwinds.

As the session resumes, drivers are advised that the spare tyres that are normally handed back can be used for another 7 minutes.

Still on softs, Ricciardo improves to 3rd with a 19.920, 0.469s off Bottas' pace.

As the drivers finally return their spare set of tyres, it's: Bottas, Hamilton, Ricciardo, Raikkonen, Verstappen, Vettel, Alonso, Massa, Vandoorne and Hulkenberg.

Taking advantage of the fact he and his teammate have the track to themselves, Bottas improves to 19.248.

As more drivers head out, Hamilton improves (19.376) but remains 0.128s off his teammate's pace. The Briton appears to be suffering understeer issues.

"We're seeing a few drivers slithering off," admits Pirelli, "not so much grip on track with little rubber laid down. But that will improve."

Having asked how he might find time in S1, Hamilton goes quickest by 0.153s, despite losing time in S2.

As Sainz goes off at T1 after locking-up, teammate Kvyat complains "something not right with the car".

Another improvement from Hamilton, the Briton stopping the clock at 18.858, the fastest ever lap of this circuit.

As Stroll goes wide in T11, teammate Massa reports a big mistake (read lock-up) in T1.

"A lot, a lot, a lot, a lot, a lot, a lot of understeer," complains Sainz.

Check out our Friday gallery from Hungary, here.