From Ski Boots to Phone Cases

How FREITAG has created a circular process to turn valuable ski boot shells into phone cases

Mobile phone cases are typically considered single-use products; they're made of virgin plastic and when the consumer changes phones, often the case no longer fits the new phone so they become redundant and end up in landfills. But...could there be another way?

FREITAG, a company that has already made a name for itself with numerous innovative upcycling projects, took up this very question, and the answer is yes! The F385 CIRC-CASE is a mobile phone case made entirely from recycled ski boot shells.

Together with the Argo Employment Opportunity Workshop in Davos, the IWK Institute for Materials Technology and Plastics Processing in Rapperswil, Switzerland, and other partners, FREITAG turns worn-out ski boots into recyclable protective iPhone® cases that not only look good, but can also protect future iPhone® models as well.

In this article, you’ll learn more about the F385 CIRC CASE protective case’s circular process, and which roles Coperion’s feeding and ZSK extrusion technologies fulfill within that process.


Ski boot shells consist primarily of thermoplastic polyurethane (TPU-R). FREITAG's process exploits this valuable raw material to full advantage. At Argo’s employment opportunity workshop in Davos, worn-out ski boots are collected, taken apart and separated from their clasps and other plastic parts.

FREITAG's CIRC CASES aus ausgetragenen Skistiefeln
Discarded ski boots are collected, taken apart and then shredded at an employment opportunity workshop in Davos to produce FREITAG’s CIRC CASES. Photo: Jesper Borg


The TPU-R reclaimed from the ski boots then undergoes several processing steps so that FREITAG’s mobile phone cases can be manufactured at the required reproducible level of quality.

First, the ski boot shell pieces are inspected using FTIR analysis to determine the exact type of plastic. The plastic parts, sorted by type and color, are then shredded into coarse plastic flakes.

At the IWK Institute for Materials Technology and Plastics Processing in Rapperswil, the flakes are then compounded into pellets. The TPU-R flakes together with necessary additives are fed via gravimetric screw feeders into a ZSK 26 Mc18 twin screw extruder where they are melted, intensively homogenized, dispersed and devolatilized before discharging from the ZSK extruder. Subsequently, the necessary pressure for fine screening builds up in the gear pump. The purified plastic melt is processed into pellets using a water ring pelletizer.


The pellets now serve as the source material for the subsequent process step: using injection molding, the F385 CIRC-CASE protective iPhone® cases are molded to order.


With its F385 CIRC-CASE, FREITAG has impressively succeeded in creating a serial application for recycled ski boot material.

Moreover, FREITAG has developed a collection system, called “Take Back”, for discarded F385 CIRC-CASEs to be recycled. F385 CIRC-CASE owners can return used phone cases to the manufacturer; these are then fed back into the circular system described above and turned into new F385 CIRC-CASE mobile phone cases, destined to protect future generations of iPhone® models.

This innovative F385 CIRC-CASE mobile phone case project garnered the Swiss Plastics Expo Award in the “Sustainability” category earlier this year. Coperion congratulates the IWK Institute, FREITAG, and the ARGO Employment Opportunity Workshop on this very well-earned accolade!

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