Used Tennis Balls Turned Into Running Shoes by a Design Student

From Court to Shoe

Manufacturers produce roughly 350 million tennis and padel balls every year. Almost none get reused. A ball loses pressure after a handful of matches and then it heads to a landfill, where the rubber, felt, and adhesive layers can take more than 400 years to break down. Only about 1% ever enter a recycling stream.

Soroosh Riazi Isfahani, a design student at the Royal College of Art and Imperial College London, thinks that is a waste. His SLICE project, submitted to the James Dyson Award 2026, turns discarded tennis balls into sneaker uppers without shredding them first.

Shredding the ball was his original approach. He mixed the granulate with natural rubber and pressed it into soles. It worked, but it ate energy and destroyed the one thing that made the material interesting: the curve of the felt, the bounce of the rubber, the bond between them. He abandoned that route.

Cut, Don't Crush

His revised method keeps the ball intact. A tennis ball is a pressurized sphere with no flat surface. It rolls, it deforms under pressure, and freehand cuts come out uneven. To solve that, Isfahani 3D-printed cutting guides. Each guide locks the ball in place and marks the blade path so every strip comes out consistent. Change the shoe size or the pattern and you just modify the digital model and print a new guide.

From a single ball he gets curved strips and caps. He shapes them over a shoe last, the foot-form used in shoemaking, and stitches them together with old racket strings. No heat, no chemical adhesives, no glue. The fluorescent yellow felt, the white stitching, and the scuff marks stay visible on purpose.

The aesthetic borrows from Freitag bags, which are sewn from retired truck tarpaulins and wear their history on the outside. Isfahani wants the same thing here: a shoe that shows where its material came from.

What Comes Next

Isfahani is already working on more complex models that combine tennis ball sections with leather offcuts. He is also exploring bags and sports accessories built the same way, and a custom service that uses balls from a specific club or tournament so each pair carries a direct connection to its source.

The James Dyson Award runs annually and rewards inventors who solve real problems with practical design. Winners will be announced later this year.