Kevlar vs Fibreglass

Hi all

I am debating whether i should by a kevlar kayay or a fibreglass one.

what is your opion and any pro’s and cons

In general… One Pro, no cons…
And that is lighter weight. Depends what boat and which lay-up you get whether it’s worth the money.

depends on the boat
"sea kayaks" aren’t meant to be superlight, they’re designed to hold up to X use.

If you’re priorities are a light sea kayak then look for one that is designed with that in mind instead of going for the lighter option.

My $.02 is that I’d rather have a glass kayak and save the $400-$800 for stuff.

Mostly it’s a matter of money, if you want option A that weighs 5lbs less and don’t mind spending the money,there you go. I don’t find that a 55lb kayak weighs that much less than a 60lb kayak at the end of the day when carrying 5lbs of stuff but a 40lb kayak is noticably lighter.

Kevlar vs Fibreglass
The problem i have is its cheaper to import the kevlar than the glass.

I don’t care about the weight issue I am after a boat that can handle the occasional knocks and scratches. I am interested to know is fixing Kevlar simular to glass

I own a ecobezhiq and a tempest 170

The boat i am looking at is the paddling perfection. Slingshot or Polarbear.




Kevlar vs Fiberglass
I own both and and would not spend the extra money for the Kevlar again.

I just had to have the best, and I believed that the Kevlar would be the strongest. I mean, hey, bullet proof vest’s are made of Kevlar - right??

My glass is much tuffer in the abuse area.

It seem’s my Kevlar has to be a little more babied, seems the Kevlar is a little flexible but the gel coat is hard, hit it just right and you have a problem.

Being a female, not trusting my own repairs in a sinkable craft, I did trust a fiberglass repair kit and it worked well, on my fiberglass.

Couldn’t find a kit to repair the Kevlar, I had to hunt marina’s to find some one to work on my Kevlar as all of them would tackle the glass and no one the Kevlar. Price went up again…

Also my Kevlar is too light, I have to carry extra weight to track well in it, no problems with the glass.

I own 8 kayaks and I would not purchase the Kevlar again from my experience with all materials.

I purchased a plastic, Perception, Shadow, loved it so much I purchased the same boat in Kevlar. Never used a rudder in the plastic, can’t keep straight with out it in the Kevlar. Not worth the extra cost for sure.

I never had to baby the roto mold plastic’s or fiberglass.

I’m 5’5", weighing in at 125lbs. and have never not been able to handle a 65lb. boat over a 43lb. boat.

I give the Fiberglass my vote.

The kevlar in kayaks is NOT
ballistic kevlar…Marketing is amazing isn’t it?

Don’t know if this is true …
… and have never seen this written anywhere. A sales person at a reputable “local” kayak shop told me that Kevlar slowly absorbs water over time and will gradually gain weight. Wasn’t trying to sell me a boat or anything, just having a general discussion on glass vs. other materials. Has anyone heard this? Anything to it?

Here’s one opinion…
From NC Kayak website:

Yes, we offer a carbon/Kevlar blend at the upgrade price of $599.00. However, we don’t recommend that you choose this option. We believe carbon and Kevlar are not the best materials for kayak construction. Carbon is generally recommended because it is very stiff, and stiffness translates into speed. Yet, carbon is brittle and does not handle impacts very well. Kevlar can take impacts, but it does not have a long life-expectancy. The sun’s ultraviolet rays weaken Kevlar. Also, Kevlar does not make a molecular bond with other materials, and with its unique properties, it will begin to separate from the rest of the kayak over time. Because of this, a kayak made from Kevlar will begin to absorb water, and will gain weight drastically. A carbon/Kevlar blend does compensate slightly for their respective weaknesses, but does not solve them. Our LT fiberglass kayaks are within a pound of our carbon/Kevlar kayaks. You get more bang for your buck with a considerably longer lifespan.

I don’t think a kevlar kayak will gain weight drastically unless it’s cracked and sitting in water all the time. I have seen water stains in a kevlar kayak at cracks in the hull but I don’t think it adds noticable weight. The amount of water in a 4" diameter stain can’t be very much.

Methinks that the weight gain story is marketing to focus on whatever is the proprietary layup of a manufacturer.

Focusing on the fabric leaves too many other variables out of the picture.

True to an extent
Kevlar doesn’t like to stick to things in the matrix as well as other materials. As such, it is “prone” to interlaminar shearing which is a gradual breakdown within the lay-up / matrix. Good epoxy or vinylester resin lay-ups minimize this, but it’s still an issue. Surf kayaks that take lots of pounding if made with Kevlar can become softer after a couple of years. Carbon / glass surf boats last longer and retain stiffness longer in my experience. Kevlar is hydroscopic and will absorb some moisture, but I believe this is insignificant really. Most kevlar boats are actually also glass or Carbon as the latter adds stiffness. I think it’s a decent material when used wisely. The inner layer of the matrix would be a better application. Where weight is primary and the other variables secondary, Kevlar is a good call. It’s just a material with pro’s and con’s, so the trick is to apply materials where their strengths are maximized.

Thanks Salty for saying that …
Yep, how many times do we have to hear that misinformation … ahhhhhh.

And another …

– Last Updated: Nov-10-06 6:15 AM EST –

This is an overview of the materials as they apply to kayaks without really going into specifics of fabric weights and weaves. Each of these needing another page each. The gentle reader should glean all needed info from this to figure some things out.

Fiberglass is stiff, strong and relatively inexpensive when compared to other exotics.
Carbon is super stiff, stronger than equal areal weight glass. It does cost a lot more.
Kevlar is amazingly strong and tough. It costs more too but the real expense is working with it. Cutting and trimming is difficult at best.

Some interesting numbers for 5.7 oz cloths.... all have similar 18x18 type weaves.

Breaking strength: 5.7 oz. E glass 225-250 lbs.
5.7 oz. Carbon (6k?) 300 lbs.
5.0 oz Kevlar 650 ! lbs.

One would think the Kevlar is the only way to go. It is and it isn't.

There are many ways to lay up a boat. It would be refreshing to hear manufacturers reasons behind why they choose to do one thing or another rather than just offer something as the end all.

Are they building with Kevlar to save weight or to have a stronger boat? (Or to make more $$$?)

Which is stronger? Glass or Kevlar?

Before my head explodes with all I have to say and do not have time to write....I will say this.

A glass boat layed up thoughtfully will take more minor bumps and grinds and will also absorb a greater amount of energy than kevlar BEFORE it STARTS to fail.If a equally layed up kevlar boat were built it would not take as much abuse before it would start to soften up .......BUTTTTT. A kevlar boat WOULD endure catastrophic force far better.

If a giant were to pick up a glass boat and wack it across a log it would probably break 1/2 - 3/4 of the way through on the first hit and fly to pieces on the second.

A kevlar boat would make a dull thump on the first hit and show some damage in the form of delamination of plys but would be mostly intact. The second hit would probably cause failure of the resin and the boat would lose it's shape at point of impact but it would still most likely stay together. It would take several more hits by an increasingly frustrated being before the boat would come apart.

This is what kevlar can picture what would happen if a jetski plowed into you to offshore or you bailed on a big set and your "lifeboat" pounded on the rocks for a set or two before getting spat out.Kevlar can provide security a non balistically layed up glass boat could not.

A quick synapsis of my personal construction opinions. Please note I do not follow the same line of thinking many of the Majors do.

I can build a super light all glass boat but I do not recommend this. The thinner glass layup is not quite as tough as the light Kevlar layup and due to the extra labor involved I would also charge the same price to build one.

If boats are going to be bounced off of rocks on a regular basis in any conditions other than blue water go for the standard glass construction. Unbelieveably tough and resistant to bump and grind damage. Still light and does well enduring the day to day stuff for a long time. Save some $$$ too.

If boat will see occasional rocks only and will not be abused with IN heavy surf / rescues with boat wallowing full of water etc. AND a light weight,stiff, super strong, safe build is the goal , go for the Lightweight Kevlar layup........ I just call it Kevlar layup.

Blue water, real potential for life threatening conditions , boat may hit a submerged rebar at speed it, MUST stay together after shark , jetski or cargo ship attack........ Go for a kevlar layup built up around the weight of a similar glass boat then add a bit. Please let me know what you are thinking / picturing.

So much to say here...... Until I really write down each scenario I am trying to describe briefly here all this might sound confusing.

Especially if you go by what other manufacturers are doing. I do not have a generic Kevlar layup. Each one is custom built based on it's intended use. Most of the added cost of a kevlar boat over a standard glass layup is labor.....Carbon does more even though it is easier to work with...... but the thread was glass vs. kevlar.

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Two boats by the same builder
Kevlar will be lighter, faster and more expensive.

Fiberglass will be heavier slower and cost less.

I like speed and since I am over the hill I also like lightness, so I’ll opt for the lighter kevlar one.



Considering that speed is a function of drag, which is identical between Kevlar and fiberglass models of the same boat, how can the former possibly be any faster than the latter?

If you’re referring to acceleration, a 5 pound difference in boat weight is ~2% or less of the total boat+paddler+gear weight, so it’s not going to make much difference there, either.

There is a slight acceleration with each stroke I take to make up for losses during the recovery ( “glide” )portion of my stroke. Given the distances that I paddle, I’ll take that extra 2% you say 5 lbs difference in boat weight gives me.

for an all glass construction wouldn’t unidirectional glass layed transversely in the mid-section be a good idea? It’s interesting to see manufacturers go through different layups. Regular heavy woven roving was standard for a glass boat. Now everything has a layer of core material with lighter glass on the inside.

Necky is doing interesting stuff reinventing the wheel but the flat bottom sections in the Chatham where there isn’t core material make for noticiable “ringing” when plunging on waves.

Have owned boats made of all
materials discussed, and I have not seen any special tendency for Kevlar to delaminate with time in my whitewater boats, which obviously take a lot of hammering. The bond of epoxy resin with Kevlar is just as “molecular” as the resin bond with properly pre-coated glass, or Nylon, or polyester/CAP. Now, if you use vinylester resin, you can get an unusually tenacious bond to CAP because the resin temporarily eats into the surface of the fibers. But vinylester bonds about the same to S-glass as to Kevlar. Millbrook is using S-glass outside, Kevlar inside with vinylester resin, and gets excellent results. Kaz could use CAP for better bonding, but he races his boats, and he apparently finds they last fine with Kevlar.

Good thread here
full of logical information. Onnopaddle, I agree with your post but would only add that the values would be for tension. Kevlar, as noted is crazy strong in tension, but very weak in compression. To g2d’s point about good bonding, I believe it’s possible to minimize inter laminar breakdown very effectively. I recall chatting with an Aerospace guy about wing to body fairings on some jets that they made of Kevlar initially to save weight. These did experience breakdown and water absorbtion, but were not structurally critical.

It’s going to be interesting to see how the new carbon epoxy airliners hold up through years of compression / de-compression. I don’t believe there’s any Kevlar in these layups, but not sure on that. Of interest is the fact that more Titanium has o be used as aluminum interacts badly with Carbon / Graphite.

Lee, absolutely. I do that in all my
boats to get some ‘hoop’ strength … also think about the seat ‘hard spots’ coming back the other way while you are sitting on it … This helps support the kevlar’s sort of weak compression from the inside out + helps boat hold its shape here too. Uni on the aft deck too.

I always like the image of a person sitting on a flower, with its uni petals radiating out from under the seat.

Yep Salty, don’t want to send the wrong
wrong message about kevlar. From my experience, I feel kevlar IS weaker in compression from a real world standpoint than what the actual charted numbers would tell you. But marry it up with S-glass and the two support each other in a wonderfully symbiotic relationship. IMO, if using carbon, go all the way with it. Otherwise a properly scheduled kevlar / S- glass layup is my close second favorite from a pound fo pound perspective Never had any problems with delamination either but using epoxy… i did call Dupont years ago about using polyester with kevlar too to get the scoop form the tech guys over there. A good description of using ‘esters’ with kevlar can be found on the Sission kayak website. Yep, kevlar can fuzz on the inside @ wear points and sort of trap water, but it still drys back out … so easy to prevent this though and just another thing that suprises me why it does not get done by the big guys.