Expanded polystyrene (helmet foam)
The material inside a cycle helmet, and the one place in this catalogue where a cleaning mistake destroys the function of the object and leaves NOTHING TO SEE.
Precautions
- Check the manufacturer's instructions
- Consider professional help
In detail
Expanded polystyrene is the liner of most bicycle helmets: polystyrene beads expanded in a mould under heat and pressure into a stiff, crushable foam. It protects by crushing, which means it is consumed rather than dented — and once its cell walls are crushed its impact management is gone. Two facts govern how it is cleaned and both are about invisibility. The helmet safety institute states that crushing is NOT ALWAYS VISIBLE and can be hidden by the outer shell, and that damage is often not apparent on casual inspection even when there are cracks in the foam. And it states that ALMOST ALL FOAMS USED IN BICYCLE HELMETS ARE DAMAGED BY PETROLEUM-BASED SOLVENTS of the kind found in many paints. Put together, a solvent that reaches the liner can degrade the thing that protects a skull while leaving a helmet that looks perfect. That is a different risk class from a marked worktop, and it is why this record carries prohibitions and no permitted method: the institute is not the manufacturer, and it says plainly that it cannot specify what is safe. The replacement rule is separate from cleaning and worth knowing: after a single impact, the helmet is finished.
Why
- Expanded polystyrene (helmet foam) is explained by Solvents and polymers
Sources for this page
Sources
Bicycle Helmet Liner Materials, and Painting a Bicycle Helmet
Bicycle Helmet Safety Institute · Credible secondary source
Relied on for: That EPS is the liner of most bicycle helmets and protects by crushing, that crushing is not always visible and can be hidden by the outer shell, that damage is often not apparent on casual inspection even with cracks present, that almost all helmet foams are damaged by petroleum-based solvents, and that the helmet is replaced after a single impact. (states this directly)
Verification: a person has read the passage relied on.
Read on — The foam liner materials page, and the solvent section of the painting page. Supports the claim as stated.
What CleaningHQ cannot answer yet
These are recorded questions about this subject that we have not yet researched to a standard we would publish.
- A permitted cleaning product and method for a cycle helmet and its liner
Last reviewed by a person on .