bicycle helmet · cork · shaping · styrofoam

Modifying a bicycle helmet to fit my head

My resistance to wearing a bike helmet has been from finding them to be giant klunky things filled with HUGE amounts of styrofoam. My head is big from front to back, but narrow from side to side. A large or extra large helmet may sit on my head without squeezing it, but can leave a lot of space on either side. So I am supposed to put a mattress full of  the included foam padding on either side to take up the space, and the whole thing ends up looking like a giant hat from the San Francisco production of Beach Blanket Babylon.

I see some motorcycle riders go by with low-profile/minimalist helmets which can’t be more than a centimeter or 2 thick. While I doubt they have an official approval for motorcycle use, I suppose it keeps the rider from getting a citation, and it’s better than wearing nothing in the event of a crash.

I usually wear a helmet for longer rides, but typically not for around town. For me, a helmet is handy for several reasons:

1) It keeps my bicycle hat from blowing off.
2) Once on a ride, a beer bottle whizzed by me at 60 mph. It just missed the back of my head. The next time a motorist or their passenger wants to throw something at me, I would prefer to be wearing a helmet.
3) It’s a good place to mount lights.
4) It offers some protection from rain, sleet and hail.
5) I can stop anywhere on a ride to take a nap and I don’t need a pillow. With the helmet on, I can rest my head on a rock slab and catch some ZZZs.
6) In the event of a crash, it reduces the chance of victim-blaming and makes your lawyers job easier.
7) If my head ever does get smacked, I would rather have something more substantial on it than a bicycle hat.

I read that helmets are not designed to protect the head in crashes exceeding the usual bicycle speed (15mph) or in a car crash. So I’m really not concerned about modifying it. It seems to me that there is not a lot of protective effect to lose.

 I am not suggesting you modify your helmet or follow my example! Doing so may destroy the protective effect of your helmet resulting in injury or death! This is only an essay of my efforts to modify a product to suit my needs!

Carving out the Styrofoam

I wanted a helmet that was light, not bulky, has a hard shell, is comfortable, covers the back of my head (remembering the beer bottle missile), is well ventilated, and did not make me look too much like a dork. I would consider it a success if I was able to go riding with it and completely forget there was anything on my head. After a lot of searching, I settled on a climbing helmet, the Mammut El Cap, which had a rather narrow profile. The large size is a bit too small for me, but I would scoop out some of the styrofoam from the inside of it until it fit. I know that styrofoam can be cut with a hot wire or knife; but how about scooping it out with a hot spoon?

I got an old steel soup spoon, my hardware store propane torch, and a leather glove to hold the spoon. First I bent the spoon so I could maneuver it inside the helmet. After heating it up, I began carving layers of styrofoam away.  It did not take long to figure out how to do this. When the spoon was the right temperature, it went thru the styrofoam like it was scooping ice cream that was just soft enough to enjoy. A gentle pressure on the hot spoon allowed it to slide slowly thru the stuff, leaving a nice rounded interior surface. I stayed downwind of the noxious fumes that were generated from the process. After several passes and reheating the spoon many times, I would put the helmet on my head and feel where more material needed removal. After I was done, the helmet fit my head without needing any adjustment pads. An average of half an inch was removed from the inside of the helmet; maybe 3/4 inch on the inside crown. It covered more of my head because my head was more than half inch deeper inside the helmet compared to how it was before. The sides of the helmet almost touched my ears. That’s when I decided to stop carving the styrofoam.

My chosen lid, the Mammut El Cap, a climbing helmet. It is quite narrow, has full ooverage, built in clips for light straps, and plenty of ventilation.


Assembling the tools

I removed the plastic adjustment strap that was part of the rear of the helmet. My head was too big for it.

After some scooping, lots of styrofoam liquifies into a small tarry patch on the spoon.



Quite a bit has been carved out. I took out a little extra and replaced the padding strips that came with it.


Cork strips along the back and sides. Replaced the pads on the inside crown.

To finish, I added self-adhesive cork strips I cut from a roll of cork meant for shelf covering. With a climbing helmet the styrofoam doesn’t extend down along the sides as much, so this adds a bit of protection and fit. They expect the main issue would be rocks falling from above.

I really like this helmet. It fits like a glove, and I forget it is on my head.  I can shake my head side to side and it does not move at all. That means I will wear it more often. I should probably wear it when driving a car too.
Not a dork.