Getting Started: Navigating the Materials Maze

Winter 2008

This is an article from WaveLength Magazine, available in print in North America and globally on the web.
To download a pdf copy of the magazine click here: > DOWNLOAD

by Alex Matthews

Traditionally, kayaks were made from sealskin stretched over a wooden frame, but now most commercially available kayaks are built from a variety of plastic-based materials.

The different materials and their respective qualities can be confusing to a prospective buyer, but the most common materials currently used are generally divided into three basic groups:

• Polyethylene
• Composites (like fiberglass, Kevlar® and carbon)
• Thermoformed acrylic-capped ABS

Polyethylene
For polyethylene, think “Tupperware”–it’s basically the same plastic. Polyethylene or “poly” boats are very affordable, and have amazing durability. Nothing else even comes close to a poly boat when it comes to absorbing big impacts or standing up to serious abuse. Poly kayaks are a little soft, and do deform over time, especially when exposed to heat (like the hot sun). They are also significantly heavier than most kayaks built from other materials, but poly kayaks require the minimum of maintenance and are extremely difficult to puncture, crack or otherwise destroy. The low price of polyethylene kayaks makes them a real bargain and the perfect first boat for many paddlers.

To recognize a poly boat, look for a duller, less glossy finish, a heavier overall weight, and for the deck and hull colors to be the same—the deck and hull are not two separate parts in a poly boat. Instead the entire shell is one continuous molded piece of plastic. This means that there is no seam in the material and no opportunity to have different colors between the deck and hull. Looking inside a poly boat will usually reveal the same basic color as the exterior, although some manufacturers use a “3 ply” process to increase stiffness and often features an interior color that is different from the outer one.

Composites
Composite boats are stiffer, lighter and shinier than polyethylene ones. They are also about twice the price! Kevlar® (a gold colored cloth made from aramid fiber) or Carbon (a black woven cloth made from carbon fiber) kayaks are lighter (typically by 5 – 10 lbs) than fiberglass ones, but are more expensive still. Composite kayaks yield the best performance on the water and are stiffer and lighter than poly. While composite kayaks are definitely subject to more damage from heavy collisions than polyethylene kayaks, composites will last for a great many years if treated carefully, and are actually far more durable than most people suspect. All composite constructions are a sandwich of different fabrics that are wetted out and bonded together by resin. Different “cores” (usually made from urethane) are sometimes included in the laminate to further increase the stiffness of a part. The outermost layer of a composite kayak is usually an eggshell-thin layer of pigmented resin called gelcoat. “Clearcoat” finishes, which allow the underlying fabric to show through, are also popular on carbon and Kevlar® kayaks.

To recognize a composite kayak, look for a high gloss finish, a seam between the deck and hull (although the hull and deck may be the same color), and a different color on the inside of the boat. The interior finish will usually display the woven fabric of the laminate or may occasionally be painted.

Thermoformed
A newer construction technique for kayak manufacture is thermoforming. This process uses a vacuum to draw heated plastic sheet material over a mold to create parts. The sheet material used is a clever mix of two different plastics: acrylic and ABS. Acrylic-capped ABS consists of a thin sheet of acrylic permanently bonded to a thicker sheet of ABS. The resulting material displays the desirable properties of both plastics: ABS vacuum forms beautifully but doesn’t have a great finish; acrylic won’t vacuum form but has an excellent glossy finish. Combined in one sheet material, the two plastics produce crisply molded high gloss parts that rival composites in visual appeal. Although more prone to flex than composites, and somewhat heavier, thermoformed boats seem to be on par with composites relative to resistance to impact, although long-term durability remains to be seen. Overall thermoformed kayaks provide a good compromise between the greater affordability of polyethylene boats and the beauty and lightness of composite ones.

To recognize a thermoformed boat, look for a finish rivaling that of a composite kayak, but expect to find more flex. The real visual clue, however, is that the interior color will be the same as the exterior, with a smooth finish unlike the more textured and different colored interior found within a composite kayak.