To all with engineering/material science background, here's what I'm trying to explore: relationship between frame, stringbed and ball stiffness that defines comfortable/soft feel on impact. Upon experimenting with different frames, strings, tensions and balls I'm coming to conclusion that relationship that gives the most comfort is following (if measured in RDC stiffness units): frame > stringbed > ball Example: from RSI string review frame = 68 RDC units stringbed = 76 RDC units @ 60 lbs I could assume, that in this setup stringbed does not give in on impact enough to soften the shock, hence "firm" or "harsh" feeling on impact. At the same time, I assume that 76 RDC stringbed is somewhat stiffer than average tennis ball, which means it more easily deforms the ball on impact. Now, I tried noodle-soft frames (such as Head Satellite Tour) with super stiff stringbed (Gosen Polylon/OGSM @ 55 lbs) and stiffer frames, such as BLX90 with softer stringbed (Polystar Turbo / OGSM @ 48 lbs) and by my observations, I would prefer stiffer frame with softer stringbed, in terms of comfort. And in no way I would choose to play with stiff tennis balls (over pressurized, firm rubber, harsh cloth and little felt) as I need very rigid surface to deform/compress them (fyi interesting article on dynamic properties of tennis balls). That's probably one of the reasons why new generation of players prefer stiffer racquets as "more comfortable": they simply offset increased stringbed stiffness (due to poly strings) and higher velocities at which balls travel which change their "dynamic properties". frame > stringbed > ball stiffness relationship as "more comfortable" is purely hypothetical, feel free to debunk or confirm it.