Design Engineering
Showcase 2020

FLEX - Flexible Folding Cycling Helmet

Design Engineering MEng
Olga Kravchenko
Modern Motion

Folding bike helmets are rapidly gaining popularity among urban commuters, due to the improved convenience they offer, despite a compromise on safety. To improve the usability and performance of these helmets, a radical new helmet design needs to be created.

FLEX is a flexible, folding cycling helmet. It utilises the RHEON™ technology to remain flexible until impact, where the helmet stiffens, absorbing energy. FLEX uses a combination of weight optimised geometries and compliant hinges to offer superior linear and rotational impact protection, improved fit on the head, while also being reusable over multiple impacts.

 — FLEX - Flexible Folding Cycling Helmet
Final design of FLEX helmet shown with optional visor.


Expanded Polystyrene is the key protective element in almost all helmets. It is effective at absorbing energy from single impacts and is very weight efficient. After a single impact, however, it loses most of its performance.

Folding bike helmets are attractive due to their improved convenience but leave much to be desired in folding capabilities and protection. A unique solution is the Hövding airbag helmet, which is discrete and very protective, but can only be used once and depends on unreliable electronic triggering. The ideal helmet needed to be passive, without the need for activation, fold very small and be very protective.

Material Technology

The helmet was designed in collaboration with RHEON LABS, using their powerful material technology: RHEON™. This is a strain rate sensitive material, that is flexible until an impact occurs, where it instantly stiffens and absorbs energy, without effecting the performance for the next impact. Through careful design of geometries, these effects can be accentuated, improving protection.

The reusability and recyclability of RHEON™ also improves on both traditional EPS and the Hövding helmet in the environmental impact, extending the lifetime of the helmet and closing the loop at the end of the product’s life.


FLEX is designed to be uniquely convenient with extreme foldability and top-level performance. The design used living hinges and topologically optimised geometry to fold so easily, it can be integrated into a hood or stuffed into any bag. The foldability and reusability are combined to make a simple and convenient user experience for urban commuters.

 — FLEX - Flexible Folding Cycling Helmet
A breakdown of the helmet’s key features.
 — FLEX - Flexible Folding Cycling Helmet
In addition to being fully foldable, FLEX can be attached to a hood and will fold naturally along with the fabric.


The project was approached using an engineering design workflow, optimising individual elements and unifying them into a cohesive design. Key steps involved: the development of an optimal folding configuration for ease of use and maximal foldability; creating weight optimised geometries, and designing a new compliant hinge for folding and greatly improving fit.

 — FLEX - Flexible Folding Cycling Helmet
Left: A full scale prototype was 3D printed out of PLA for fit and user testing. Right: Injection moulded RHEON test samples for impact testing.
 — FLEX - Flexible Folding Cycling Helmet
Left: Linear drop rig used for validation. Right: Render of planned testing using the RHEON LABS rotational test rig.


The helmet was validated using an industry standard testing rig and was shown to outperform traditional EPS helmets in a single impact, with no reduction in performance over multiple impacts. The helmet can be optimised further for either weight reduction or increased protection, creating a range of options for future development.

 — FLEX - Flexible Folding Cycling Helmet
Expected use cases for the FLEX helmet are urban cyclists.


This looks great! When can I buy it?

Billy Wu

This is beautiful work!

Michael Hofmann

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