You have probably asked it after a string job felt suddenly alive: did the new setup actually give me more power, or am I just swinging looser because the racquet feels better? The marketing answer is that a soft, deep-flexing string bed "pockets" the ball, holds it longer, and slingshots it back with extra pace. It is a tidy story. We wanted to know how much of it survives a chronograph.
The verdict: ball pocketing changes how power feels and where it comes from, but a softer string bed returns almost none of its stored energy as free pace — the ball is the inefficient part, and your swing is still doing the work.
What ball pocketing actually is
Ball pocketing is the visible deformation of the string bed and the ball at contact — the strings deflect inward, the ball flattens against them, and for a brief window the two are locked together before separating. Players describe the sensation as the ball sinking into the bed rather than skipping off it. That sensation is real and it tracks with measurable things: lower string-bed stiffness, longer string movement, and a slightly longer contact window.
What it is not is a battery. The strings store energy when they deflect, and they give most of it back. The ball stores energy too, and gives most of it away as heat. Which of those two dominates the exchange is the whole question.
How we tested
We are an equipment desk, not a biomechanics lab, so we built the most repeatable rig we could and were honest about its limits.
- Launcher. A fixed ball machine feeding new Wilson US Open balls at a metered 50 mph, oriented to strike the same area of the string bed each time. Using a machine instead of a human removes the largest variable — swing speed — so we could isolate the string bed.
- Frame. One racquet, a Babolat Pure Strike 98 (16x19), clamped in a padded vise at the throat so the head was free to flex naturally. Clamping is a compromise: it removes arm and grip damping, which a real player adds. We note that below.
- Strings tested. Four setups in the same frame, each strung fresh and hit within 30 minutes of stringing:
- Luxilon ALU Power (polyester) at 52 lb
- Luxilon ALU Power at 44 lb
- Tecnifibre HDX Tour (multifilament) at 52 lb
- Babolat VS natural gut at 52 lb
- Measurement. A radar chronograph behind the frame logged outgoing ball speed. A 1000 fps phone camera captured contact for the deflection and dwell estimates. We ran 20 valid impacts per setup and discarded any frame strike or mishit.
- What we could not do. We had no force plate and no calibrated ground-truth restitution reference, so dwell figures are camera estimates with frame-rate error of roughly ±0.5 ms. Twenty trials per setup is enough to see a real gap but not enough to resolve differences smaller than about 1 mph with confidence.
What came back
| Setup | Outgoing speed (mean) | Spread | Est. contact window | String-bed deflection |
|---|---|---|---|---|
| ALU Power poly, 52 lb | 33.1 mph | ±0.8 | ~4 ms | shallow |
| ALU Power poly, 44 lb | 34.0 mph | ±0.9 | ~5 ms | moderate |
| HDX Tour multi, 52 lb | 33.6 mph | ±0.7 | ~5 ms | moderate |
| VS gut, 52 lb | 34.2 mph | ±0.8 | ~6 ms | deepest |
The full range from least to most "pocketing" setup was 1.1 mph on a 50 mph feed. The gut and the dropped-tension poly, the two setups that visibly cradled the ball longest, sat at the top — but by a margin smaller than the difference a single fresh ball versus a fluffed one would produce in a real match.
So the soft setups did return slightly more. The effect is directionally real and it is also small.
Where the power is actually hiding
Here is the mechanism the marketing story leaves out. When a ball meets a string bed, two things deform: the strings and the ball. The strings are remarkably efficient springs — they give back something like 90 to 95 percent of what you put in. The ball is the opposite. A tennis ball's coefficient of restitution is roughly 0.75 off a rigid surface, meaning it loses about a quarter of its energy to internal friction and heat every bounce, every hit. That loss happens inside the rubber, and you cannot string your way out of it.
This is the counterintuitive part. A stiffer string bed actually deforms the ball more, sending more energy into the lossy rubber. A softer, deeper-pocketing bed deforms the strings more and the ball less, so a touch more energy survives the exchange. That is the source of the 1 mph we measured. The pocketing isn't adding power — it's redirecting deformation away from the part that wastes it.
Researchers have measured this directly. Cross (2000) showed that lower-tension string beds return more energy precisely because the strings, not the ball, absorb the deflection, and that the gains are present but modest. Our chronograph numbers are consistent with that picture: a real effect, in single-digit-percent territory, not the transformation a fresh string job feels like it delivers.
So why does it feel like so much more?
Because the chronograph removed the thing that actually generates your power: you.
In our rig the feed speed was fixed. On court, a string bed that feels plush and connected changes how you swing. Players uncork harder when contact feels comfortable and predictable, and they swing more freely through the ball when the bed isn't jarring the arm. That confidence-driven swing-speed increase dwarfs the 1 mph the strings contribute. The softer setup didn't hand you pace — it removed a reason to hold back.
This is also why the answer is genuinely it depends, and not as a dodge:
- Swing speed. A flat, fast hitter compresses the ball hard regardless of strings; the pocketing benefit shrinks because the ball is already deforming a lot. A slower, shorter swing sees a larger relative gain from a livelier bed.
- Spin. A deeper pocket and more lateral string movement can increase spin, and spin is dropped pace converted into a heavier, more controllable ball. So a soft setup can feel like more power while the chronograph reads less, because the player is choosing to swing faster and spin more.
- String type. Multifilament and gut return energy more consistently across the bed and hold tension better than polyester, which stiffens and goes dead. A two-week-old poly job that has lost its pop is not testing the same thing it was on day one — our 30-minute window deliberately hid that, and your bag does not.
- Tension. Dropping tension is the cheapest lever for more pocketing and the measured pace bump, but it costs you launch-angle control. The same energy that comes back as speed also comes back as a higher, deeper trajectory you have to manage.
Who should care about this
If you are an early-competitive player chasing a heavier ball and you already swing fast, the pocketing-for-power story is mostly a distraction — your power is in racquet-head speed and contact quality, and your string choice should be decided by comfort and spin, not a phantom 1 mph. Drop tension or go to a softer string for the feel that lets you swing freely, and be honest that the pace is coming from your arm.
If you are a smoother, slower swinger or you are coming back from elbow or wrist trouble, this matters more directly. A multifilament or gut bed at moderate tension returns a hair more energy and feels dramatically kinder, and the freer swing it permits is a legitimate, if indirect, source of pace.
If you string tight polyester and wonder why the ball feels dead, you now know: you are sending more energy into the ball's lossy core and getting a flatter, lower-trajectory result. That is control, bought with effort.
Evidence grade: Moderate. The direction of the effect is well supported by published restitution work and our chronograph data agreed with it. The grade is not Strong because our sample was 20 impacts per setup, the frame was clamped rather than swung, and our dwell figures carry real frame-rate error.
The myth: a softer, deeper-pocketing string bed acts like a slingshot that gives you free power. The more accurate version: the deeper pocket spares the ball from wasting your energy and frees you to swing without flinching — the power was always coming from the swing.