Raw Carbon Grit and the Science of Spin: Why a Rough Face Adds Rotation

Coach Yoshi

Owner of Pickleball Lab

Published October 24, 2026

About 32 min read

19757 characters

Raw Carbon Grit and the Science of Spin: Why a Rough Face Adds Rotation

Why do raw carbon paddles put spin on the ball? I've gone one step beyond "because the surface is rough" and laid it out using ideas from the science of friction (tribology). This article covers how roughness (grit) turns into spin, how it wears down, and the spin standard that changed in October 2026.

I'm Coach Yoshi. I've played tennis for 15 years, and ever since I discovered pickleball on a trip to LA in 2026, digging into what's inside the gear has become a hobby of mine. Something close to the feeling of the ball biting into the strings when you hit topspin in tennis also happens on a paddle face. But what's going on underneath is a little different. Tennis strings also add spin by sliding sideways and springing back (snapback), but a paddle face doesn't do that. A paddle's spin is determined almost entirely by friction. This article is a follow-up to the Raw Carbon Material Guide (Beginner's Edition). It's not about "what to buy" but about "why the ball spins."

Physics First: Why Does "Grip" Create Spin?

In a word, spin is rotation created by friction (grip). Let's look at it a little more carefully.

When you brush the face upward at the moment the ball hits it, the ball's contact point tries to slide across the face. Friction pulls the contact point in the direction opposite to that slide. Because the contact point is off the ball's center, this force turns the ball around its center, and that creates rotation (spin). It's the same idea as getting spin in tennis by "brushing" the ball.

There are 2 key points here.

Friction adds spin only while the ball is sliding. Once the spin builds up and the contact point stops sliding, the spin stops increasing. This is the "spin limit" that comes up later. A rougher face can stop the slide sooner, so the difference tends to show on shots where the ball meets the face at a shallow, brushing angle.
The brushing angle matters. If the ball meets the face head-on (perpendicular), there's little sliding to begin with, so not much spin is created. The faster you swing and the more you brush the ball, the more the contact point slides, and friction turns that into spin. But if you brush it too thinly, the ball leaves the face before the slide can be stopped, so you actually get less spin. Even with the same paddle, the amount of spin changes a lot when your swing changes. (On the serve, it's against the rules to add spin with your hand or paddle when you release the ball; you may put spin on the ball only at the moment the paddle makes contact. This is rule 7.B.2 in the USA Pickleball 2026 Official Rulebook. For serve basics, see the Complete Serve Guide.)

Three-step side-view diagram of a ball hitting a paddle face: 1, the ball slides across the face; 2, friction slows the slide while spin increases; 3, once the slide stops, spin levels off. It also notes that roughness matters more the shallower the ball meets the face, and that the difference is small when the ball meets the face at a steep angle

The diagram is based on the Tennis Warehouse University (TWU) experiments (2022 and 2023) that I introduce later. What stops in step 3 is the sliding, not the spin.

💡 Coach Yoshi's Tip You'll often see the explanation that "a longer dwell time (the time the ball stays on the face) means more spin." But TWU's experiments didn't measure the time on the face itself. According to TWU's explanation, unless the face springs back sideways the way rubber does, spin levels off once the contact point stops sliding, and it barely increases after that even if the ball stays on the face. TWU's experiments also didn't look at how much the softness of the core affects spin.

Why "Raw Carbon" Is Rough: Fiber Texture and Peel Ply

So where does the roughness (grit) that creates that "bite" come from?

Raw carbon is a carbon face finished without a covering of paint. Carbon fiber comes in grades, and among raw carbon paddles you'll often see products that advertise Toray's T700 (T700S). How the fibers are laid out varies by product, for example aligned in one direction or woven. A regular carbon face is finished smooth after molding by sanding or painting the surface. Raw carbon skips that finishing, so the texture of the fibers and the fabric imprint left in the surface resin during molding remain as they are. That's where the roughness comes from.

Broadly speaking, there are 3 ways that roughness gets made.

How the grit is made	How it works	How it wears
(1) Peel ply (release fabric) transfer	A release fabric applied during molding is peeled off at the end, transferring the fabric's texture and the fractured resin surface onto the face	Relatively long-lasting, since it's a "mold" imprinted into the surface layer
(2) Rough paint or spray applied afterward	A gritty paint or coating is sprayed or brushed on after molding	Wears off easily, since it just sits on top of the surface
(3) The fiber texture itself	Leaving the face unpainted exposes the texture of the fibers near the surface (the weave, if it's woven)	Relatively long-lasting, since it comes from the fibers

It makes the most sense to think of a raw carbon face's roughness as a combination of (1) and (3). Because it's roughness built into the structure of the material, not roughness added on top with paint, it's said to last longer than paint.

Raw carbon faces suddenly multiplied around 2021 to 2022 (in August 2022, Pickleball Studio wrote, "In the last year, you have seen them pop up everywhere"). They're often discussed together with thermoforming, which molds the face and core into a single unit with heat and pressure, but grit (a property of the surface) and core construction (how the inside is built) are two different things. I cover what's inside in Foam Core Paddles Explained.

Grit Wears Out: Why Spin Drops When the Face Goes "Smooth"

This is where tribology (the science of friction) gets interesting. The more you use grit, the more it wears away, and eventually it flattens out. The peaks on the surface get worn down by contact with the ball and become gentler. Then the slide is harder to stop, and spin drops, especially on shots where the ball meets the face at a shallow angle. That's why the spin performance of a raw carbon paddle is said to be "consumable."

That said, even if you feel the spin has dropped, it doesn't necessarily mean the face is worn down. When sweat or dust clogs the texture, the ball also has a harder time gripping. I explain how to clean the face in Paddle Lifespan and Care.

How fast it wears depends on how the grit is made. The owner of Pickleball Studio, a U.S. review site, broke it down like this in a 2022 article.

Roughness added with paint (paint grit) wears off very quickly. The owner writes that he has made a paint grit paddle smooth in just a few days of hard hitting.
Textures and coatings added afterward usually last longer than paint. But how long they last varies by product, and you can't tell from the spec sheet.
Raw carbon roughness lasts noticeably longer than paint grit or added textures. In the owner's spin tests, too, raw carbon paddles consistently post high numbers.

The owner also writes that, as of 2022, there was still no surface that never wears down with use.

As an answer to this wear problem, more and more faces are being called "Durable Grit." These are faces built so their roughness lasts longer than raw carbon, and the method varies by manufacturer, such as mixing particles into the resin, using ceramic, or spray-on coatings (Pickleball Effect, 2026). The Engage Axiom, which our store carries, also uses a carbon face that Engage calls Durable Grit. For how to choose and the signs it's time to replace a paddle, see the Raw Carbon Material Guide.

Diagram comparing 3 ways of making a paddle face's roughness (grit) and how easily each wears down. Roughness added afterward with paint or the like wears down easily, the fabric imprint on raw carbon lasts longer than paint, and durable grit is a face designed to last even longer. Every face eventually wears down with use

💡 Coach Yoshi's Tip An easy way to check for wear yourself is to run the pad of your finger across the face. If the gritty feel it had when you bought it is gone and it's starting to feel slick, that's a sign the grit is wearing down. Before you decide, wipe the dirt off the face once and then check again. Two basics for keeping the face from getting damaged: don't scrape it on the ground, and put it in its cover when you're done playing.

The Spin Limit: Even with a Rougher Face, Spin Has a Ceiling

This is the part I most want to get across today. A rougher surface doesn't mean spin keeps increasing forever.

As friction puts spin on the ball, at some point the contact point stops sliding. That's because the spin gets fast enough that the contact point comes to rest relative to the face (it grips the face). Once the slide stops, friction can't add any more spin. This leveling off is the spin limit (the maximum spin friction can produce). Step 3 in the first diagram shows this state.

The ones who tested this experimentally were TWU, run by the tennis retailer Tennis Warehouse. In a 2022 experiment, they fired balls at about 3 to 7 m per second (about 7 to 16 mph) at a clamped paddle and measured the spin on the rebound with a camera. When the ball hit at an angle steeper than 45 degrees to the face, paddles with very different static coefficients of friction, such as about 0.31 and about 0.69, produced almost the same spin. A difference appeared only when the ball hit at an angle shallower than 45 degrees, in a brushing way, and there the paddle with more friction produced more spin. TWU believes that most real shots fall into the first category.

The role of grit (roughness) is not to raise the ceiling but to get you closer to it even on shallow, brushing contact
Once you reach the ceiling on steeper contact, differences in roughness have almost no effect on spin

In Pickleball Studio's 2022 measurements as well, a paddle whose face roughness was well below the limit in the standard at the time recorded the most spin the site had measured (1,851 RPM). It's an example showing that roughness numbers alone don't determine spin.

💡 Coach Yoshi's Tip "So is raw carbon pointless, then?" Not necessarily. In TWU's experiments too, when the ball hit the face at a shallow angle, the face with more friction produced more spin. TWU itself, however, believes that at those angles spin drops a lot to begin with and such contact is rare, so in normal play differences in face roughness hardly show up. As I see it, the job of a rough face is to make it harder to lose spin in situations where the ball meets the face at a shallow angle, like a thin, brushing shot. When the face wears down and gets slick, it becomes harder to put spin on the ball in those situations.

The Ceiling Set by the Rules: From October 2026, USA Pickleball Measures "Spin Rate"

Spin also has a limit set by the rules. The USA Pickleball (USAP) rulebook (3.D.5 in the 2026 edition) prohibits a paddle's hitting surface from containing anything that lets a player put excessive spin on the ball, such as rough texturing, sandpaper characteristics, natural or synthetic rubber, or paint textured with sand.

Of these, for "natural or synthetic rubber" (3.D.5.d), the rulebook doesn't give a reason. TWU's experiments show how different it is from a paddle that spins the ball by friction alone. TWU attached a table tennis rubber (1.0 mm thick, no sponge) to a paddle, fired balls at it at about 6.3 m per second (about 14 mph), and compared it with an uncovered face. The rubber face produced almost twice the spin and a rebound about 14% faster. According to TWU's explanation, rubber flexes sideways and springs back (snapback), so it can add spin beyond the limit that friction alone can reach.

How a hitting surface is judged against the rules by the numbers changed on October 1, 2026. Through September, there were upper limits on surface roughness and coefficient of friction. Roughness was measured in 6 directions on one face, and the average Rz (the height difference between peaks and valleys) had to be 30 μm or less and the average Rt (the largest peak-to-valley difference) 40 μm or less (with no single measurement above Rz 33 μm or Rt 44 μm). Friction was tested under ASTM D1894-14, with a kinetic coefficient of friction of 0.1875 or less (Equipment Standards Manual, January 2025 edition). Review sites sometimes use Ra (arithmetic mean roughness), but USAP's standard was based on Rz and Rt.

From October 1, paddles newly submitted for certification must have a spin rate of 2,100 RPM (2,100 revolutions per minute) or less as measured in testing. Surface roughness and coefficient of friction are no longer upper limits; they're now measured as values of record.

Diagram showing how USA Pickleball paddle certification shifts from upper limits on surface roughness and coefficient of friction to judging new certifications from October 1 by a spin rate of 2,100 RPM or less. It also shows that paddles already certified follow the standards in effect when they were certified

In the test, a specially marked ball is fired from a launcher at a clamped paddle, and software calculates the spin rate from footage shot by 2 cameras. As the TWU experiments in the previous section showed, roughness numbers and actual spin aren't necessarily proportional. So the approach has shifted from judging spin indirectly through roughness to measuring the spin itself.

However, the new standard isn't applied retroactively. USA Pickleball states, "All certified paddles must comply with the equipment standards that were in effect at the time of certification." In other words, paddles certified through September were certified under the roughness and coefficient of friction standards, and paddles certified from October onward are certified under the spin rate standard. I also covered how the announcement unfolded in the [July 2026] World Pickleball News Roundup.

UPA-A certification, used on the pro tours (such as the PPA Tour and MLP), also caps spin at 2,100 RPM. UPA-A requires a paddle to stay at or below 2,100 RPM for its entire usable life, not only when new but also after a test that simulates a well-used paddle (ABI) (UPA-A Paddle Specifications v26.6, July 2026). I've summarized the differences between the 2 certifications in USAP vs. UPA-A Certification.

RPM Numbers Change with How They're Measured

Spin rates (RPM = revolutions per minute) are often featured on review sites too. But each site measures them differently. For example, Pickleball Effect uses a radar (Stalker Pro 3S) to measure 10 serves hit with maximum spin and takes the average as the paddle's value. In an article updated in October 2026, it says the average paddle is around 2,000 RPM and only a small share at the top exceeds 2,100 RPM.

USA Pickleball's 2,100 RPM is a figure from a test in which a launcher fires balls at a clamped paddle. Even though both say "2,100," they use different yardsticks, so a review number above 2,100 doesn't mean the paddle violates the standard. Pickleball Effect itself also asks readers not to compare its numbers with those from other sites. Compare numbers only within the same test.

And in the end, the biggest variable is your swing. The maximum spin friction can produce is determined by the speed and angle at which the ball meets the face and by the spin on the incoming ball, and in TWU's experiments it didn't change from one paddle face to another. The roughness of the face only makes it easier to reach that limit. What raises the limit itself is how you hit the ball.

Summary: Raw Carbon Grit Is a Face That Helps You Avoid Losing Spin

The one point I wanted to get across in this article is this.

The roughness of raw carbon doesn't increase spin without limit. It stops the ball's slide sooner and brings you closer to the maximum that friction can produce. The difference tends to show on shots where the ball meets the face at a shallow, brushing angle. That's why, as the face wears down, it gets harder to put spin on the ball in those situations. This is why it's called "consumable." On the rules side, too, since October 2026 new paddles are certified by spin rate (2,100 RPM or less) rather than by roughness.

Once you know the physics, you can consciously check how spin changes between hitting the ball flat and brushing it thinly. The next time you're on court, try hitting with the same paddle while changing only the angle of contact, and compare. Knowing what's inside your gear makes the next shot a little more fun. That's probably also why I can't climb out of this rabbit hole.

For how to choose the material itself, see the Raw Carbon Material Guide (Beginner's Edition); for the differences between carbon and fiberglass, see Carbon vs. Fiberglass; and for sorting out power and control, see Control vs. Power Paddles. For the paddles our store carries, each product page describes how the face is made (raw carbon, durable grit and so on) and its certification status. Choosing with an understanding of what's inside makes picking a paddle even more fun.

If you have questions like "Does this paddle put a lot of spin on the ball?" or "My paddle face is getting slick. Is it time to replace it?", feel free to ask me (Coach Yoshi) on LINE. You can add us as a friend through Pickleball Lab's official LINE account. You can also add us with the green "LINE Official" button at the bottom right of the screen.

References

Author

Coach Yoshi / Owner of Pickleball Lab

Former international ski competitor and active tennis coach. Discovered pickleball in LA in 2026 and has play-tested more than 100 paddles from Japan and around the world. Pickleball Lab is Japan's exclusive authorized distributor of Engage Pickleball (as of May 2026).

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