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Background: A year or so ago, I noticed that a pair of bib shorts had a spot of deterioration on one of the thigh panels. Basically it was a round spot where the outer weave had apparently disintegrated. I thought about it and decided that a drop of chain lube must have damaged the fabric. Meanwhile, the shorts were washed in the same way that I've been doing this for years. The thing is... I continue to get these spots of deteriorating fabric. It's only on the front leg (thigh) panels and nowhere else.

Considering the location and pattern of the fabric damage, the only thing that seems logical is sunscreen dripping from my face to the shorts. The problem looks like drops that expand and grow from the original drop.

So, what damages lycra? Or cycling clothing in general?

I have quite a bit of cycling and other sports gear made of similar fabrics which have not had this problem. This is really a puzzle. The gear is expensive and I'd just as soon that this not happen.

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What type of Lycra? Polyster or Nylon? –  Joe Philllips Oct 27 '10 at 15:23
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4 Answers

up vote 6 down vote accepted

Lycra (spandex) comes in two forms as far as I know: polyester-lycra and nylon-lycra. Polyester based lycra will withstand harsh conditions whereas nylon based lycra will not.

Polyester is hydrophobic, meaning it does not absorb water. This means that when it is dyed, only the color of the dye dissolves into the fabric (not any water-base), making the dye permanent. Nylon® possesses hydrophilic qualities (that is, it absorbs water). Its inability to repel water causes the fabric to swell and ultimately weakens the molecular structure. The dyestuffs used on nylon® tend to oxidize, a reaction which is catalyzed by light. The microscopic effects range from color fading to complete degradation of the polymer matrix. This is why the colors fade in nylon-lycra® swimsuits over time, but do not fade in polyester-lycra® swimsuits (Man-Made Fiber Yearbook, August 2000).

See the Fabric Information Guide for more information

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Is it always in the same spot? Do you have a piece of gear that rubs in that spot? I know I have a jacket and if I'm not careful with the zipper I get wear spots really quick just above my crotch. It sounds kinda like what you're describing.

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No, not the same spot. It was one spot, now it's several. Only on the front thigh section. I ruled out toxic sweat since I have thoroughly impregnated the entire set with sweat on rides in the summer. The problem looks like expanding drip marks in a few areas. –  user313 Oct 26 '10 at 4:55
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How old are the pants? If they are more than say 5 years old and you use them a lot, my guess would be that the sun's UV rays are causing the elastomer's to break down and slowly deteriorate. Same thing happens to old rubber bands (lycra is, to be overly simplistic, just rubber and cotton woven together). It would make sense that they would first appear on the top of your thighs as that is the spot that is in the most direct sunlight.

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Note the original question: "Background: A year or so ago," –  user313 Oct 26 '10 at 4:50
    
@wdypdx22, "Background: A year or so ago, I noticed that a pair of bib shorts had a spot of deterioration on one of the thigh panels." Do you mean this was the first time you noticed the deterioration, or was this when you bought the pants? Two different things. –  Ben Oct 26 '10 at 20:13
    
if it were UV, the shoulders or the butt panel would deteriorate before the thigh panels. –  David Dec 2 '10 at 5:49
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I've wiped excess sunscreen countless times on my cycling shorts with no ill effects. Same goes for sweat, chain oil and miscellaneous grime picked up on roadside repairs.

My cycling clothing wears out from friction (simple things like a camelbak slowly rubbing holes in backs of jerseys, to obvious ones like accidental high-speed contact with asphalt) and from general wear & tear. Lycra definitely loses its stretch over time too. And watch out for loose velcro straps, they can tear up lycra and jerseys during a ride or in the wash.

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Not friction. I added to my original post. –  user313 Oct 26 '10 at 5:00
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