After starting to play pickleball with a wooden or inexpensive “beginner” paddle, you realize that like many others, you have become addicted to the sport and want to buy your own “performance” paddle. These paddles may range from about $50 to over $300, coming in a wide range of shapes, sizes, materials, weights, and thicknesses. Besides price, what really differentiates one paddle from another? Moreover, why would one paddle perform better than another?
Many pickleball paddle manufacturers try to differentiate their products from others by making claims that are often confusing and contradictory, especially to non-technical consumers. Some manufacturers claim that the materials and design of their paddles are better than others because they are lighter, stronger, stiffer, or more aerodynamic, resulting in more speed, power, control, a larger sweet spot, more forgiving, etc, etc, etc. Who should you believe? What are the real differences among paddles considering their materials and construction? Let’s see if the science can tell us.
Major Components and Basic Fabrication
Most modern pickleball paddles start from a panel that consists of a “sandwich” of face sheets that are adhesively bonded to a core material (Figure 1). Composite materials are typically used for the face sheets because they provide a very high stiffness at a very low weight. Common pickleball face sheet materials include fiberglass, carbon fiber, graphite, and Kevlar composites. The core material is typically a honeycomb as these structures absorb more energy than foams or tubes. These honeycomb cores consist of regular six-sided hexagonal cells that can be made from aluminum foils, extruded polymer (polypropylene), or Nomex papers. The basic concept of a honeycomb sandwich panel is that the face sheets provide bending stiffness whereas the honeycomb core provides shear stiffness. We will examine what this means and how this affects pickleball paddle design and construction in the following sections.
Besides the shape and weight distribution of the paddles, the materials and construction of the composite honeycomb panels are the key differentiators among paddles on the market. While it is possible to purchase high quality military- or aerospace-grade composite panels made in the USA, paddle manufacturers will typically purchase these panels from specialty manufacturers in Asia. This is necessary since the manufacturing and lamination of the face sheets and honeycomb cores requires expensive equipment, facilities, and materials that must be amortized over several products. Use of such equipment for paddles alone would make the cost of the paddles exorbitant. Consequently, there are only a handful of companies that perform the final manufacturing and assembly of their paddles in the USA, using honeycomb composite sandwich panels manufactured overseas. Many of the less-expensive paddles are completely produced in Asia due to their proximity to the panel manufacturers and availability of low-cost labor for final assembly and packaging.
The basic components of a pickleball paddle are shown in Figure 2. The construction process starts from a large honeycomb composite panel that may or may not have a base paint or coating. The basic paddle shape, or blank, is then cut using a computer numerical control (CNC) mill or waterjet cutter. Logos, final paint, and/or coatings are then applied to the blank. The handle is then glued to the face sheets at the handle location, and balance weights may be added to the handle or to the edges of the paddle face before the edge guard is adhered. The handle rubber or leather over-wrap is then attached to the handle and the fully assembled paddle is packaged and ready for sale. In the following sections we will examine the various materials and construction techniques that go into honeycomb composite panels to see how they affect paddle performance.
The Honeycomb Core
The innermost layer of a pickleball paddle is the honeycomb core, which is comprised of a regular array of hexagonal (six-sided) cells (Figure 3). The reason that bees build their hives with a honeycomb structure has been a topic of debate since 36 BC. Finally, in 1999 the mathematician Thomas Hales proved that a hexagonal honeycomb could fit the most area with the least perimeter. For bees this means that they can store a maximum amount of honey inside the honeycomb cells while producing the least amount of wax to create the cells. For pickleball players this means that a honeycomb will enclose the largest volume of empty space (air) with the minimum amount of material. Honeycomb panels are therefore ideal for pickleball paddles as they are among the lightest structures occurring in nature.
As mentioned above, the honeycomb core must provide shear stiffness to the paddle. The importance of shear stiffness is illustrated in Figure 4. If you stack thin strips of wood or cardboard on top of each other and apply a bending load (P) to them, they would easily bend, resulting in a large deflection (δ1) at the loading point (Figure 4a). If you examined the ends of the stack where the load was applied (Figure 4b), you would see that each strip slides or shears against each other. If you prevent the shear movement by clamping or gluing the strips together, the stack would become much stiffer, resulting in a smaller deflection (δ2) at the loading point (Figure 4c). The honeycomb core works in the same way by constraining differential shear motion between the top and bottom face sheets. The honeycomb shear stiffness is determined by its material properties and thickness.
Another requirement of the honeycomb core is that it must separate the top and bottom face sheets of the pickleball paddle. Why is this important? Figure 5 shows a cross sectional view of a pickleball paddle, where tf is the thickness of the face sheets and hc is the thickness of the core. Each face sheet has an elastic modulus (Ef) which is a material property related to the material stiffness.
It can be shown that the bending stiffness (Kb) of the panel can be approximated by:
Kb ≈ ½ (Ef tf hc2) Equation (1)
The importance of the bending stiffness (Kb) was discussed in a previous article, “How Large is the Sweet Spot”. Here we performed a vibration test of a pickleball paddle and showed that the size of the sweet spot is determined by the so-called trampoline mode. Furthermore, the frequency and amplitude of the trampoline mode is directly related to the panel bending stiffness Kb, where the trampoline effect will diminish with increasing panel bending stiffness. Pickleball paddle manufacturers can therefore make a stiffer paddle by merely increasing the thickness of the core material (hc) while using the same face sheet.
To illustrate, certain models of pickleball paddles are often available in two thicknesses – 13 mm and 16 mm. Which one should you pick? Since the paddles are identical, it is likely that they use the same core materials and the same face sheets. Therefore, by using Equation (1), we can take the ratio of the bending stiffness of one paddle to the other. This indicates that the 16 mm thick paddle is 1.5 times stiffer than the 13 mm paddle. A mere increase in core thickness of 3 mm results in a 50% stiffer paddle! The 16 mm paddle would therefore be categorized as a “control” paddle and the 13 mm paddle would be a “power” paddle (see our article, “Power vs Control Paddles”.
Finally, the honeycomb core must be capable of absorbing the impact of the ball and rebounding without crushing or undergoing permanent deformation. In general, thicker honeycomb cores must have smaller cell sizes because the longer webs are more prone to buckling. In fact, a common failure mode of honeycomb composite panels is crushing of the core, resulting in debonding of the core from the face sheet. This would cause a “dead spot” in the paddle. “Control” paddles will have stiffer cores, whereas “power” paddles will have more compliant cores.
Popular core materials found in pickleball paddles include aluminum, Nomex, and polypropylene.
- Aluminum has been used since the 1940’s for lightweight honeycomb aircraft panels. Of the three materials discussed, it has the greatest shear strength and rigidity and offers the highest strength-to-weight ratio. It is suitable to sustain and absorb high impact loads; however, if the loads are too high, the aluminum webs may buckle, resulting in debonding of the core from the face sheets. Paddles made with aluminum honeycomb cores will tend to be stiff; however, the increased stiffness may allow the paddles to be thinner.
- Nomex is a tradename by DuPont, which is usually associated with the fire-resistant suits worn by race car drivers. Nomex is a man-made material that is lighter but costs more than aluminum. It is manufactured in paper form and is made rigid by use of a phenolic resin coating. While it is one of the lightest materials used for honeycomb cores, it does not have the shear strength, rigidity, or impact tolerance of aluminum. Paddles made with Nomex cores will tend to be less stiff than those made with aluminum cores.
- Polypropylene is a type of thermoplastic polymer where the honeycomb structure is extruded into the pattern of regular six-sided hexagonal or cylindrical cells. It is less stiff than either aluminum or phenolic-coated Nomex; however, it is more resistant to shock and provides a greater degree of vibration damping than either aluminum or Nomex. Paddles made with polypropylene cores will therefore have greater rebound capability and will transmit less vibration back to the player’s arm than either aluminum or Nomex core paddles.
The Face Sheets
The face sheets provide a surface to contact the ball and provide bending stiffness to the paddle. They are constructed from a layup of composite materials that are stiffer and stronger than metals at a fraction of the weight. Composites consist of fibers, such as fiberglass, carbon, Kevlar, or graphite that are held together with a matrix or binder material, such as epoxy. The material stiffness or elastic modulus of the fibers can be several orders of magnitude greater than that of the matrix material, depending on the volume fraction of the fiber to matrix material in the composite lay-up.
The diameter of the fibers and their lay-up (or weave) can have a significant effect on the surface finish or smoothness of the face sheets. Typical fiberglass (E-Glass) and Kevlar fibers have diameters in the 10-25 micron range. For purposes of comparison, the diameter of a human hair is 75 microns! Carbon and graphite fibers have smaller diameters of 5-10 microns. Like grades of sandpaper, panels made from larger diameter fibers will tend to have rougher surfaces than those made from smaller diameter fibers.
Most pickleball paddles use fibers that are woven together into sheets that are pre-impregnated with a binder material, such as resin or epoxy. These sheets, called pre-pregs, are available in several different patterns such as plain, twill, and satin weaves (Figure 6). The type of weave is selected based on the desired surface finish and the expected loading of the composite sheet. A plain weave coupled with a larger fiber size, such as fiberglass would produce a rougher surface. Such a surface might be ideal for putting spin on a ball. A satin weave coupled with a smaller fiber, such as graphite, would produce a smooth surface. The smoother surface might be ideal for a “control” paddle that is relatively unaffected by the amount of spin your opponent puts on the ball. We discuss friction, face sheet materials, and their effect on topspin in our article, “How is Topspin Generated?”
Finally, the material stiffness or elastic modulus of the fibers has a significant effect on the bending or flexural stiffness of a composite panel. Equation (1) above shows that the bending stiffness is linearly dependent on both the face sheet thickness and elastic modulus. Figure 7 compares the flexural stiffness of similar panels made from carbon/graphite fiber, aluminum, fiberglass, and Kevlar. The flexural stiffness is denoted by the slope of the curves, with the steepest curves corresponding to the stiffest materials. As indicated, carbon fiber and graphite are very stiff and have about the same bending stiffness as aluminum. Kevlar is a tradename by DuPont that is well-known for being used in bullet-proof vests. It has about the same flexural stiffness as fiberglass, but it can absorb a far greater amount of flexural strain without breaking than fiberglass.
Putting It All Together
Pickleball paddle manufacturers have a great deal of flexibility in determining the performance characteristics of their paddles by mixing and matching the various face sheet and core materials. For example, a thin but lightweight paddle might be desired so that the player can have greater swing speed and maneuverability with less arm fatigue. An ideal paddle might have a carbon fiber face with a thin aluminum core. Other players may want a stiff paddle that is more forgiving, so they might choose a thick paddle with a carbon fiber face and a polypropylene core. Still other players may want a paddle capable of putting a lot of spin and velocity on the ball, so they might choose a thin paddle with a fiberglass or Kevlar face and polypropylene core.
There are literally hundreds of different combinations of face sheet and core materials available using different weaves, thicknesses, geometries, and coatings. It is therefore no surprise that there are hundreds of different paddles on the market to choose from. Pickleball players should therefore try out several different paddles that use different combinations of face sheet and core materials to find a paddle that is ideally suited to their style of play and physical capabilities.
