by Anders » Tue Jun 15, 2010 2:00 pm
Copied from the web but I agree on the conclusion... also the outer shell will deteriorate due to UV exposure or so they claim**.
"Helmet manufacturers and the Snell Foundation suggest replacement after about 5 years.
Impact protection comes from the outer shell, the styrene inner shell, and the comfort lining. The styrene inner liner crushes as it absorbs energy. The comfort liner compresses until it bottoms out against the styrene. Glues, resins and other materials used in helmet production can affect liner materials, and general liner deterioration and helmet degradation can result from hair oils, body fluids, cosmetics, and normal "wear and tear."
From past experience there will probably be a noticeable improvement in the protective characteristic of helmets over a five year period due to advances in materials, design and the standards. Therefore, regardless of wear, you will probably want to replace your helmet every five years"
**A 10 year warranty is the industry standard for polycarbonate sheet products though the working life is normally considerably longer. Actual performance depends on individual applications and local environmental factors, but 20 years and over is now becoming common. Most thermoplastic materials do suffer slow deterioration as a result of UV exposure, usually this initially manifest itself in a gradual yellowing of the sheet rather than a reduction in the mechanical properties.
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