Did anyone else hear Wilander during the second set of Djokovic vs. Berdych say that the balls get less kick off the second serve fresh from the can?
I couldn't believe it, but why should I be surprised.
i wouldn't go into physics here, but i've always prefered serving a second set with a fluffier ball.
Maybe it stays 1ms longer on the strings to get some additional rotation, compared to the fresh ball jumping off it right away.
Unconsciously i always take the fluffier one for second serves, maybe it's just subconsciously not wanting to overcook it, dunno.