Glass, kev, poly, thermoform sea kayaks

Glass, kevlar, poly, thermoform sea kayaks…

Why one over the other? If you had a choice for one of the materials which one would it be and why? Is there much advantage of having stiff material (kevlar) boat over lets say more flexible thermoform?

thanx for any input.

Oh not again…
KEVLAR IS NOT STIFF! Quite the OPPOSITE. I’m gonna let the others help here and simply wish you well with your search.

Kevlar is stiff!!! :wink:

What he said… NM

Glass, kevlar, poly, thermoform
I’ve never used thermoform, so I can’t speak to that at all. I paddle the other three in everything from flatwater to currents and breaking surf, and I’ll attempt to give you “my” observations. You have to be pretty careful with poly in hot temperatures, due to its tendency to form dents at any pressure points. A few hours in the hot afternoon sun in NC strapped on Thule saddles (or whatever rack) with any reasonable snugness can result in dents. Other than that, a little more weight than others. The frayed ends left from little scratches may have an effect on speed, but performance characteristics overall seem to me to be just fine. Once it’s had its life of use and the hull starts softening at pressure points and the bottm of the hull starts warping a bit in areas, you have a slug of a kayak. Keep it out of the sun when out of use (this will end its life with intended performance characteristics in very short order), don’t slide it over cement or rocks and you will greatly extend its useful life as well as maintaining its speed by avoiding countless frayed ends all over the thing.

Obviously you don’t want to scratch up your kevlar or fiberglass either, and it’s still best to keep it out of the sun, but they don’t seem to be prone to the dents and softening. Between fiberglass and kevlar, for myself as a seakayaker, I don’t find any difference besides what “to me” is a trivial amount of weight, say 45lbs vs 52 lbs. I know the P&H website used to advertise carbon/kevlar boats as having the ability to be made as strong and stiff as fiberglass (not stronger) resulting in less weight. I really like that their site also pointed out the optimal load weight for their kayaks. It essentially let you know that the extra weight could lead to better performance based upon kayak design. Maybe their use of materials is significantly different than some of the others, who knows? Simply put, I’ve never been on the water and thought to myself “I wish this boat was kevlar vs fiberglass” or vice versa. I don’t find a “meaningful - to me” difference. Just my observations (well-tested in my paddling conditions). I’m sure others may have different observations/opinions. Take it all in and do what makes you happy. I know from my experience the general public is more impressed by kevlar, but I also know it can be surprising and impressive to people when someone paddling poly proves more capable than others in composite. Who cares about these non-performance related characteristics? Who knows? I’m convinced these are pretty strong factors to many, and unfortunately very rarely admitted - I think it would avoid many heated debates. These are all real reasons for people’s choices. It’s all about feeling happy about it.

I’ll take one of each thank you !
Each has it’s place, except I know nothing about “thermoform” except a few years back, one outfitter was going to stop carrying a certain brand, because they were coming apart at the joints.

What is your prime use going to be?

If it happens to be dropping it on rocks or pulling over oyster bars, go with the poly




– Last Updated: Jun-12-08 1:25 PM EST –

Fiberglass (epoxy-resin in fiberglass cloth): Stiff. "Easy" to repair. Looks good. Has a long life, Expensive (due mostly to material and labor). (Concider this the "baseline" material.)

Kevlar (epoxy-resin in kevlar cloth): Stiff. Just like fiberglass except it's harder to repair. It's a bit lighter than fiberglass and significantly more expensive.

Poly (melted polyethylene beads): Inexpensive. Takes abuse well. A bit heavier than fiberglass. Has a shorter life. Not as good looking as fiberglass. (Still, it's a proven material and it's better than 20 years ago.)

Thermoform (heated ABS-like plastic sheets): Lighter than fiberglass. Cheaper than fiberglass. Might hold up to abuse. Looks like fiberglass. Probably scratches like fiberglass. May be hard to repair (I don't know). More expensive than poly (for no clear reason). (I suspect that it allows manufacturers to sell kayaks that look like fiberglass for less money than fiberglass and for more money than poly.)

In my opinion:

For most people, kevlar doesn't provide sufficient benefit for the extra cost over fiberglass.

For most people, thermo doesn't provide sufficient benefit for the extra cost over poly (unless the "better" looks are worth it).


Kevlar and fiberglass are "composite" because they use two materials: epoxy resin (plastic glue) embedded in some sort of cloth made from kevlar or glass "threads".

thickness matters
don’t forget that the thickness of the thermoformed plastic OR kevlar will determine how stiff the boat is. Different manufacturers use very different thicknesses of material.

"Material Matters"
Here’s a basic article on various hull materials and their attributes:

Good Luck!


If you can’t tell it doesn’t matter .
Go paddle the boats, if you can’t tell the difference don’t spend the money.

Did anyone mention weight?
Doesn’t matter in the water. Matters a lot loading and unloading. I poly,glass,and carbon. Carbon is 1st choice for weight; poly is for rocks and surf. Glass doesn’t get used much.

think about this also
Consider who made the boat because there will be variances in composite or plastic cross sections depending on the manufacturer.

Why doesn’t weight mattter in the water?
Why doesn’t weight mattter in the water?

Hull design is what matters in the water
Displacement, wetted surface area, length to width. With kayaks, heaviest to lightest is a range of maybe 20 lbs,30 max.Once in the water, that is negligible. On your back is a different story.

There are good uses for all of the
materials. Kevlar for racing or long portages. Thermal for durability, weight, and ease of care, fiberglass for strength, appearance, stiffness. Roto for cost and toughness. I use my rotomolded valley for the pool and surf, my P&H Cetus Glass for longer paddles or camping, and I am building a Skin boat for Greenland techniques and day tripping. You must ask yourself how you intend to use the boat and if you have a budget. If you are on a budget forget kevlar, if you plan on being hard on your boat forget kevlar. If you plan on racing, you might only want to consider kevlar. If you plan on paddling rocky rivers and leaving your boat outside, you might only want rotomolded. If you are handy and appreciate traditional paddling, you might want to make your own boat. For open water sea kayaking, you might want glass or thermalformed. If my P&H came in Eddylines thermalformed material, I think that would be the best of both worlds possibly. I like the functionality of the Eddyline boats, but their backdecks are too high IMO. If you go with thermalformed, look carefully they are all not the same. I think Valley’s rotomolded sea kayaks are outstanding boats at great prices. You get the durability of roto and the design of glass/kevlar. The lines and workmanship make the boat look like glass. I think they are a great first or last boat.As I mentioned before, the only way you might improve it for the cost would be to thermalform it out of Eddylines process. Good luck, I hope some of this was helpful.

Last boat? Is there such a thing?
I think i have it in the PBW Rapidfire.

Depends on the use …
If you want a boat that responds instantly then weight (mass) does matter. Usually only a big issue for surfers, slalom racers, racers in general. Accelleration is dependent on the mass of the boat, if you need rapid accelleration you want a very light boat. My waveski weighs 14 lbs, my surf kayak weighs 22 lbs and is considered heavy by competitive kayak surfers.

For most people…

– Last Updated: Jun-12-08 1:18 PM EST –

The weight differences are generally only about 10 pounds or so. (Eg, Kevlar is about 10 pounds ligher than fiberglass and fiberglass is about 10 pounds lighter than polyethylene for the "same" hull.)

For most people, where light-weight has a big value is carrying/lifting the boat (as String said). The other thing to keep in mind is that a longer kayak is harder to move single-handed than a shorter kayak of the same weight. (If you always have two people to carry the boat, the weight/length don't really matter for carrying it).

On the water, most people won't feel any difference between those 10 pounds.

For people who are racing (as seadart said) light weight -does- matter. For racers, almost any advantage, even small advantages, is worth it even if that advantage is expensive.

Cover your poly boat!
“leaving your boat outside, you might only want rotomolded”

You’d best keep all boats covered, including poly (maybe, especially, poly).


“If you go with thermalformed, look carefully they are all not the same. I think Valley’s rotomolded sea kayaks are outstanding boats at great prices.”

While poly boats could be concidered as being “thermoformed”, it appears that term is typically used for another material/method, namely ABS-like plastic). These boats are made from thin sheets of plastic that are pressed in heated molds. This method produces a boat that looks like a fiberglass boat.

Polyethylene boats are created from polyethelene pellets that are melted in a mold that is spun around (hence “rotomolded”. As far as I understand, this is the standard way poly boats are made. (This method/material strikes me as being very similar to “Royalex”, which has been used for canoes for years.)

Valley’s polyethylene boats do have a good reputation but everybody’s poly boats are better than they were 20 years ago.

How about this?
Same boat in plastic vs. fiber or kevlar? In particular, let’s take the Tempests that come in both plastic and fiber/kevlar option.

I’m really interested in this, not trolling here, as I’ve heard/read opinions that are entirely contradicting each other -:frowning:

Ignoring the minimal weight difference and the huge price difference, what else is there?

Would one or the other go faster on flat water (assuming new and not much hull damage to the plastic to slow you down)? How about in rough water - would the stiffer fiber/kevlar hulls make a difference?

I just got my first fiber/kevlar boat after paddling plastic and I seems to see differences in small chop - the plastic boat sort of went thru it with minimum vibrations/movement felt in the seat. In the fiber boat I felt evey little wave hitting the bow from the front/side with the hull reacting to the waves. My guess is the plastic boat just flexes and eats-up small disturbances where the stiffer composite boat does not. But since the two boat shapes were quite different, it just might be due to that (WS Tsunami 145 with very little rocker, V-hull and hard chines vs. 17 foot P&H Outlander with plenty of rocker, almost flat bottom and soft chines).