How tell Kevlar from Fiberglass

-- Last Updated: Aug-27-06 2:47 AM EST --

I got to wondering, how can you tell a kevlar kayak from fiberglass? Can you tell from looking at it? Kevlar is in the form of a weave fabric too, right? On sea kayaks, is it usually outerlayers of fiberglass cloth and inner layers of kevlar cloth?

Um, non-destructive tests only please.

Paul S.

pick it up

Look at it. Weigh it.
Kevlar is yellow. Fiberglass is clear.

Read manufactures specs and then weigh the boat.



If it stops a bullet
it’s Kevlar

Weight wouldn’t distinguish
difinitively between kevlar and a light glass-only layup. Bohemian, I’m requesting non-destructive tests only ;-). Ok, I guess if it’s kevlar then the bullet’s still a non-destructive test. But if it turns out to be just glass :-0.

Paul S.

Context and data

– Last Updated: Aug-27-06 10:26 AM EST –

I was filling out the warranty last night and I noticed the inspection slip that came with the boat said "Kevlar." I paid for fiberglass. Two shop guys looked the boat over with me when I bought it, one with 11 yrs experience. He commented specifically that all his boats are fiberglass because they are easy to repair.

Specs say fiberglass 64 lb, kevlar 56 lb. Brought the family scale to the garage. Stood on scale. Then shouldered boat and stood on scale. Says boat weighs 50 lb!. I was thinking the boat felt light even before I weighed it. It really feels light now ;-). I did have the foot pegs removed, but not the rails. They were the kind with the plastic lift rods. I put in about 4 inches of minicel in it's place. I'm guessing maybe minus 3 lbs at the most for the foot rest change. So either my scale's way off even on a delta measurement, or light fiberglass layup, of kevlar, or some of each.

The boat is lime green on white. The cloth is a little yellow tan inside the cockpit on the hull side, but I wouldn’t say straw color. It is distinctly darker under the deck. If I shine the flashlight inside the cockpit, under the deck, I can see the lime green coming through, but only with the flashlight. It’s still early in the morning so not much natural light in the garage. The rear bulkhead between the day hatch and the aft main compartment looks brown with the rear hatch cover on, but definitely clear with it off and some light in there. I’d say the bulkhead for the day hatch is definitely not Kevlar.

On inspection at purchase, I saw some hair lines in spots in the cloth that looked like a very small puzzle piece pattern. Could those be the stress cracks typical with Kevlar? I also see some straight hair lines now up to about 2” long. Those may be scratches though from gear against sand. I’m not sure. I've had the boat for almost 2 months.

I was hoping for a really definitive test involving no destruction. Probably if I saw a new Kevlar boat and a glass-only boat side by side. WCSKS next month. I can also drop by the shop where I bought it on the way up.

These kinds of things happen to me every time I get analytical about the stuff I buy. It’s a curse.

You won’t be surprised by my next post, “Kevlar vs glass at same price.” If they cost the same, which would you want?

Paul S.

Call the factory
Give them the serial number. Ask them what the boat is made from.

Kevlar vs fiberglass if same price
There were heated discussions on this subjec if you search the archives. But first, read this FAQ.

The bulletproof stuff is Kevlar 29.

– Last Updated: Aug-27-06 11:57 AM EST –

This is the ballistic fabric and is NOT used for boat building. Correction .... recreational and non-head-of-state boat building : )

Kevlar 49 is for boats ...... please remember because the bullet proof thing is really incorrectly overplayed in media stuff.

Kevlar 49 also comes in green,red,orange, blue and purple.
Fiberglass also comes in black too.

I power read those last night
Thanks swordfish, it’s well worth pointing that out. I saw the FAQ when reading back posts last night. It’s good. I was thinking though, sometimes people argue A is better than B when they mean they can’t justify the extra cost of B. That’s a little different than saying A is better entirely on technical merits. So I thought I might pose the question aside from cost. Admittedly, most who are trying to decide fg vs kev are probably not thinking so much about cost, so maybe no addional info or point of view to that question.

Thanks again. I totaly appreciate the pointers.

Paul S.

Might look @ the edge of one of the
hatches or the the deck cut out for hatch … you will be able to see ‘kevlar’ color there. This will let you know.

Lots of incorrect information about
materials in that blurb … especially about carbon … really drives me up the wall when I read info like that … just rehashed and misinterpreted views gleened from magazine type informationa and ads. Love the use of the word “They”

sorry… just venting.

A lot of “Kevlar boats” only have Kevlar in the hulls and not in the decks…

Kind of cheating…

Tan color around the hatches and combing
I used a miror. I can’t get a look at an edge of the cloth. It’s finished off nice with the cloth butting up to the hatch rims. The color is much more tan though for about a half inch around the hatch rims. Around the cockpit combing, it’s tan and smooth for about a half inch out, like a glue or resin layer over the cloth. You can’t see the cloth at all for a half inch around the combing, and very different texture than the cloth, not shiney, not patterned, monotone tan. I’m wondering if the resin has a tan tint. Or maybe the hatches and combing are re-enforced with extra kevlar and the kevlar is sanded under and around the combing. Who knows. I will call W.S. Not sure if I’ll get through though.

The boat feels sturdy and performs fine, so not too concerned. Definitely interested though. Maybe I’ll email flatpick and get his take. I’ll probably see him at WCSKS anyway.

Paul S.

Thats probably the filler used w/ resin

– Last Updated: Aug-27-06 6:09 PM EST –

to bond the parts in and fill gaps.
Another way to see and 'edge' is to remove a piece of hardware ( foot braces Grayhawk : ) and have a look @ edge.

Not much help unless you have done it before ... but a 'kevlar' boat will have a lower frequency tone to it when you knock on it. Easy to tell believe it or not.

I removed a screw, and
also looked carefully at the skeg box. Not much edge surface area to look at in the screw hole. The skeg box itself looks very tan brown. There is some cloth sticking out of surface which is white. Doesn’t mean there isn’t yellow cloth too though. It looks to me like there is tan pigment in the resin. If not, then I’m guessing kevlar. But I’m inexperienced of course. Interesting on the lower frequency tone, probably because of more flex in kevlar.

I’m hoping it’s kevlar. I wouldn’t be as comfortable with a 15 lbs light glass-only layup. Though for my use for now: lakes, slow deep rivers, sometimes with rocky (meaning river rock or stones) shores, ocean and bay mostly around sandy beaches; might be just as good.

This has been a good oportunity to really get to know my boat. It’s one thing to look around out of general curiosity. Quite another, for me anyway, to be trying to solve a problem or answer a question.

Paul S.

you really know how to kill a joke

bo, that was bad advice
Now I have two 1/2" holes in my boat. I should have used a 22.


why do you want to know?