Pirelli expects three-stops Sunday
"Everybody has faced extremely tough conditions during the first day of running in Malaysia," he said. "Luckily our tires have performed faultlessly so far, but of course the real work lies ahead of us as the drivers put their cars into qualifying and race trim.
"Today, the drivers tried out the evolution of our hard tires and their response was generally favorable, although we need to be careful that we don't end up with tires that are too conservative."
As for Sunday's race, Hembery feels most teams will be forced to stop three times for tires.
"Given how harsh the conditions were today, we've been pleased with the way that things have gone and we're expecting a three-stop strategy for the race.
"Obviously there will be some interesting tactical calls from the teams tomorrow when it comes to deciding which tires they will choose to qualify on. This is just going to add to the spectacle of what is sure to be a fascinating race."