The Formula 1 rookie got his first taste of the new car at Barcelona on Wednesday, after team-mate Pastor Maldonado had been very impressed by the car on day one.
Bottas was just as positive about the new car, and he believes that the main improvements are with the handling at the rear end.
"I had a smile on my face after the first proper run, and that was purely because I feel we have made an improvement," Bottas told reporters at Barcelona.
"It feels better as a whole package, but one area I could point to where it's better is rear end cornering grip and getting out of the corners.
"The traction and rear grip has improved and I think that will help us on long runs."
Bottas said that while it was hard to measure how much better the new car is than last year's FW34, the difference is significant.
"The first impression - when I remember the test I had last year with the FW34 - I immediately felt improvements [this year]," he said.
"It's difficult to say how big the improvement is, but you can really feel it and you can see it in the data.
"The car is pretty good to drive straight out of the box. It feels like it's a little bit easier to drive so for doing consistent lap times it's really good."