Fiberglass is so named because it has glass fibers embedded in resin. If you change the resin material, the finished product is still called fiberglass.
Do helmet manufacturers ever specify the resin used in the helmet shell? Heres is a sample of resins that can be used:
CPF - Isophthalic polyester resin, CVF - Vinyl ester resin, SPF - Isophthalic polyester resin, SVF - Vinyl ester resin, SGF - Orthophthalic polyester, SFF - Isophthalic polyester resin,
SPW - Polyester resin, epoxy, phenolic, poly/vinylester, cynate ester, bmi. The aging and durability characteristics will, of course, vary among the various resin selections.
As you might guess, statements about general fiberglass durability are meaningless unless you know something about the materials used in its construction. Further, the actual construction and curing process of the finished material plays a huge role it its durability.
The process of resin hardening doesn't stop after it first becomes rigid for many resins. Over time and heat it continues to harden to the point of brittleness. This process is accelerated if there is no seal coat to delay out-gassing of the plasticizers in the resin. Surface color plays a part in the aging process as well. Dark colors in the sun heat much higher than light reflective colors and metallic finishes retain heat longer due to the embedded metal particles.
I've also seen DOT approved helmets made of injection molded plastic, as well.
The Helmet manufacturers promulgate confusion among consumers by obscuring details.
Do the manufacturers purposely select materials that will degrade rapidly over time? And then, specify routine replacement "for safety reasons"?
Do they simply confuse buyers in order to promote sales and profit figures? (can't be too safe now, can we?)
Since the manufacturers pronounce that helmets do deteriorate with time, then shouldn't you replace your helmet every month to achieve maximum protection? Even going to the manufacturer recommended replacement interval implies a loss of protection.
Personally, I WANT the helmet to break up on impact and absorb as much impact energy as possible. I don't care if it falls apart in the process. It just needs to stay together long enough to distribute the energy not absorbed to the styrofoam liner that cushions my skull. That is the problem with the current Snell testing, as it focuses on the survival of the helmet instead of the human head it is supposed to protect.
There might be some places to have a helmet reupholstered out there but if you find that there isn't many, it is probably due to liability reasons.
I agree with eurban on this point. You change anything the manufacturer tested to comply with regulations, and you assume compliance responsibility. One lawsuit will put the upholsterer out of business. Few will risk their livelihood.
Old (define old?) fiberglass boats often used polyester (styrene monomer) resin because of it's economics. This resin is known to be brittle even right after initial cure. Further, lamination techniques and curing processes vary with the specific product being made. I assert that old boat anecdotes are pretty meaningless in a helmet discussion.
As far as risking your noggin... You do that every day, helmet or no. There is always risk. You have to learn to manage risk. If you want to minimize risk, stay off the bike and never leave your bunker. I suspect that on the risk scale of measurement, wearing an old helmet is not very far away from a new helmet. If the crash is severe enough, it won't matter anyway. But, I suspect the new helmet will look better after the crash than the old one.
IMHO
Cheers,
Cheers,