Soundbounce: Tennis Balls That Quiet the Room

Some objects have a sound we all know by heart. The "pock" of a tennis ball hitting the sweet spot of a racket is one of them. Mathilde Wittock decided to take those bouncing, ringing balls and ask them to do the opposite: quiet down the rooms they're installed in. Her project is called Soundbounce. Behind the playful name lies genuine research into sound absorption, and that's what interests me here.

A designer hypersensitive to noise

Mathilde Wittock is a Belgian designer based in Brussels, trained in industrial design and then biodesign at Central Saint Martins in London. She describes herself as an eco-designer and materials researcher. Yet the starting point for Soundbounce wasn't primarily environmental. It was about sound, and it was deeply personal. In an interview with ICON magazine, she explains that the project grew out of her own sensitivity to noise. She calls herself "hypersensitive to noise," and saw the tennis ball as a way to tackle the problem.

For her thesis, she had imagined a sensory chair designed to engage touch, smell, hearing, and the way the body feels a space. She then worked with a center for highly sensitive people, and it was while interviewing them that one requirement became clear: the material also had to absorb sound. Speaking with the United Nations Regional Information Centre, she points out that design is usually associated with the eyes, and asks: "what if it were for the ears?" She even claims noise pollution as her area of specialty.

Why a tennis ball absorbs sound

A tennis ball is a hollow rubber core covered in felt, a blend of wool and nylon glued on very firmly. For recyclers, that's a headache: the felt is hard to separate from the rubber and can't be recycled. For an acoustic project, it's an asset. ICON directly credits Soundbounce's absorption qualities to this combination of rubber and felt.

The principle is the same as for porous absorbers like foams and wools. When a sound wave hits a fibrous material, it sets the air between the fibers in motion, and that friction turns a small part of the acoustic energy into heat. The more fibrous the material, the stronger the effect, especially in the mid and high frequencies. Low frequencies, on the other hand, call for thickness or mass.

Most reuse programs shred the rubber and burn off the felt. Mathilde Wittock believes that kind of transformation degrades their technical properties, while the shape and makeup of the ball lend themselves, in her view, to tactile and acoustic uses. So she keeps the half-spheres almost intact.

What the numbers say

When it comes to performance, several claims are making the rounds. On its Material Source listing, MWO Design, the designer's studio, states that the material absorbs up to 97% of sound at certain key frequencies. The description published for Design September in Brussels mentions effectiveness in the mid and high frequencies. The MaterialDistrict platform describes strong absorption across a wide frequency range, while noting that results vary depending on installation conditions. It lists typical uses as offices, libraries, classrooms, and indoor public spaces, anywhere the goal is to cut reverberation and keep speech intelligible.

That makes sense: consonants, which carry most of what makes speech understandable, sit in the mid and high frequencies. An absorber that works well in that range can clean up a noisy room, even if it lets the bass through.

I have to be upfront, though: I couldn't find a published test report anywhere, with absorption coefficients by octave band, an αw rating, or an NRC, the kind of data normally supplied for an acoustic panel. The 97% figure doesn't specify which frequency it refers to. MaterialDistrict notes that the designer works with universities on materials and acoustics research, and the technology is patent pending. Detailed curves would be invaluable for acousticians who might want to specify it.

283 balls per square meter, and not a drop of glue

Production is almost entirely by hand. The balls, donated by clubs, are cut by hand along the white seam, stripped of their logo, and dyed with eco-friendly dyes. They're then pressed into perforated frames, with no glue or fasteners. Each square meter (about 10.8 square feet) uses roughly 283 balls, which according to the designer amounts to the equivalent of 8.5 kg (about 19 lb) of CO2 put to good use. Each ball works like a pixel: patterns are possible, and custom RAL colors are available on request.

The collection includes a lounge chair, screens, benches, and wall panels, and the material can also cover ceilings and curved surfaces. According to CNN, a lounge chair takes around 500 balls and three to four weeks of work. In October 2025, Mathilde Wittock even designed the players' benches for the European Open tennis tournament in Brussels, using balls collected from clubs in Brussels and Wallonia and cut by a sheltered workshop employing people with disabilities.

Skipping the glue is no small detail. It means a panel can be taken apart, a ball replaced, a pattern changed, and above all, the shells can be sent off for shredding at the end of their life, to be turned into rubber playground mats.

A sound resource of 300 to 400 million balls

Figures vary by source, somewhere between 300 and 400 million tennis balls produced worldwide each year, with only about 1% recycled. Mathilde Wittock, a tennis player herself, points out that a ball takes some two dozen steps and five days to make, yet lasts only about nine games at the professional level, the time it takes for the internal pressure to drop. The Wallonia-Brussels Tennis Federation handed over its entire stock, around 100,000 balls, enough for nearly nine months of production.

After the ball, the root

Soundbounce isn't a one-off experiment. With Soundwall, presented at the University of the Arts London, Mathilde Wittock developed acoustic tiles grown from the roots of fast-growing grasses. These foam-like tiles also absorb mid and high frequencies, and their textures reproduce sound frequency patterns. She says she wants to build a team of materials scientists and designers to develop sensory, ecological acoustic solutions for interiors.

This project fits into a trend I follow closely on this blog: acoustic materials made from what we used to throw away. I wrote about it with the fleece that silences the open office, and with QUIET, the silent tableware for cafeterias. And if you've ever wondered why an empty room sounds so lively, check out does a tidy room "resonate"?

A material you also hear with your fingertips

As someone who spends a good part of my time making noise with objects, I love the reverse idea: one of the most sonic objects around, repurposed to bring calm. Soundbounce has a sensory approach, a circular logic, and solid physics on its side. What it still lacks, at least publicly, is detailed measurement data to win over acousticians. Hopefully the designer's university partnerships will make that data available soon.

What about you? Would you sit on 500 tennis balls, or cover your living room wall with them for better acoustics? Let me know in the comments.