After selecting the proper class of kayak the next most important choice to make is what material the kayak is made of. Material selection is very important because it has a direct impact on both the weight of the kayak and its performance. There’s a myriad of material choices out there but we’re going to try to make this as simple as possible by grouping the materials into three general categories of increasing lay-up grade: roto-molded plastic, thermal form plastic, and composites. Let’s get into the details by considering the same kayak in each of the three different lay-ups.
Roto-molded plastic kayaks are made of polyethylene or other plastic pellets. The manufacturing process involves heating these pellets within a spinning mold to melt them and force the plastic outward into the shape of a kayak. The process results in a one-piece plastic kayak without a visible or mechanical seam. The roto-molded plastic lay-up will generally be the heaviest of the three and the least expensive. It will also be the least stiff and you can usually feel the hull of the kayak flex (or oil-can) a little bit when you pound through waves. Roto-molded plastic kayaks tend to handle abrasive wear very well over time and most can be easily repaired by plastic welding (this is the case for polyethylene but not all plastics). One should take care not to store these kayaks in direct sunlight because they are susceptible to degradation and fading. Roto-molded plastic kayaks get you on the water at a low cost.
Let’s jump to the other end of the spectrum and explore the world of composites. Composite kayaks can be made of fiberglass, Kevlar, carbon fiber or a hybrid of these materials. In most cases these kayaks are manufactured by laying composite cloth over a wooden mold of the hull and deck, wetting the cloth out with epoxy, and letting the two pieces harden. The hull and deck are then faired, gel-coated, and fastened together by a seam. The involved processing and exotic materials makes composite kayaks the most expensive lay-up around but with many perks. The composite layup has the potential to be the lightest of the three lay-ups. Other processes such as using foam core and vacuum bagging techniques will shed additional weight from a composite lay-up. Composites will always be the most stiff (this is especially true of a carbon or carbon-hybrid kayak) and thus provide the most efficient performance and least flex. Abrasive wear shows as cosmetic gel coat scratches which can be easily repaired or left alone. Composites are very durable, easily repairable (especially in the expedition environment), and can last a lifetime if properly cared for. This is the Mercedes lay-up!
The thermal form plastic lay-up offers a great compromise between the roto-molded plastic and composite lay-ups. There are many types of thermal plastics out there (e.g. Carbonlite 2000) but most are a derivative of acrylonitrile butadiene styrene (ABS plastic). The manufacturing process involves pressing sheets of ABS plastic over a hot mold to create the deck and hull. These two pieces are then joined at the seam. Thermal formed plastic kayaks are typically lighter than roto-molded boats and in some cases they are lighter than composites. Also, they are much stiffer than their roto-molded versions but not quite as stiff as a composite lay-up. These traits provide for a nice mix of light-weight performance at an affordable price. The jury is still largely out on the longevity of the thermal-form material but it seems like most of these kayaks are holding up well. They certainly are less susceptible to oil-canning than the roto-molded boats and the thermal formed plastics are more temperature stable.
In summary, you can expect both the weight of the kayak and the weight of your wallet to decrease proportionally with each increase in material grade. Likewise, each increase in material grade will result in an increase in the stiffness of the kayak and improved performance. The biggest material myth that I want to dispel is that a plastic kayak is more durable than a composite kayak. I have found composite kayaks to handle as much abuse as plastic kayaks over the years. Both certainly have their nuances with respect to durability and longevity but I will reserve discussion on the specifics of how to care for your kayak for later. Look to into the thermal form plastics to get a good mix of light-weight performance at an affordable price. The table below provides a further summary.