Just as with most man made things, motorcycle helmets have a shelf life. A helmet loses its effectiveness over time. To understand why, how and when, we need to first understand the structure of a helmet.
The Outer Shell is the external lightweight ‘plastic’ part of the helmet. It is mostly made from some polycarbonate made from polycarbonate, fiberglass, carbon fiber, Kevlar or a combination of these materials. It is the first point of contact with any external collision and is designed to prevent penetration in case of abrasive collision. It is the most solid part of the helmet and thus determines the shape of it.
TIP: Whenever you spot a crack on this part, your helmet is no longer helpful, because it cannot protect you in any subsequent collision. Meshing the crack together with an adhesive (super glue) or as a thin wire DOES NOT mend it.
The impact absorbing liner is the next layer after the outer shell. Ordinarily, this is an extended polystyrene (EPS) foam layer and is biodegradable. You can see it when you remove the comfort lining of your helmet. This is what absorbs the shock in case of any impact. Its main task is therefore to cushion your head from the impact. It is flexible and a bit rigid. It is not too rigid (because then it beats the essence of being shock absorbent) but has some rigidity to prevent full contact.
TIP: With time (storage and use), this layer hardens and loses its ability to protect your head from any impact. It becomes another hard layer that you will be colliding with in case of impact. This is what we mean when we say the helmet has ‘expired’. You can find out the viability of this layer by checking;
To see if it has hardened
For any cracks, chip or dent – This could be there even if the outer shell is perfectly intact. It is advisable that every time you drop your helmet, however lightly, you check for a crack, a chip or a dent on this layer.
The date of manufacture of the helmet. This is ordinarily on a sticker attached to this layer. A helmet’s shelf life (all factors constant) is 3 to 5 years post manufacture.
In case you notice any of this, however small, its best you replace your helmet.
The last layer id the internal comfort layer. This is what your head is directly in contact with. It’s designed for comfort and is thus made from cloth. This layer is removable.
TIP: Remove this layer and wash it regularly. This helps with the integrity of the EPS layer because it absorbs the sweat on your head, which could easily permeate to the EPS layer and reduce its shelf life.
Now that you know about helmet expiration, be sure to keep it safe and replace it before its time.