Thermoforming: The New Kid on the Block

*This article appeared in Wavelength Magazine in the Spring of 2009

When Dustin Hoffman was advised that “plastics are the future” in the 1967 movie “The Wavelength MagazineGraduate”, none of us at the time had any idea of what was coming. In 1975 I watched as the entire whitewater market did a side slip from fiberglass to rotomolded polyethylene in the space of about two years. Is there another revolution going on today? Perhaps similar, but it won’t be quite the same. As long as there is a market for low-end kayaks, polyethylene will still dominate because of lower material and process labor costs. Thermoforming, or vacuum forming does offer some quite interesting options to paddlers who possess a taste for quality and can afford the less then rock bottom prices. Before we go there however, lets talk about what exactly thermoforming is and how it differs from other plastic manufacturing processes.

First the Material

Most of the “plastic” kayaks you see today are made of rotomolded polyethylene, a tough, flexible and relatively soft plastic. In this process the resin pellets are pulverized into powder and the appropriate amount is poured into an aluminum two part mold that is then closed and basically ‘tumbled’ in an oven. This causes the powder to melt and coat the inside surface of the mold. The ‘tumbling’ and heating methods vary widely. Within some minutes, a rubbery hot kayak emerges from the mold and is supported while it cools and shrinks.

The thermoforming process requires an intermediate step that can involve quite a variety of different materials. Before a boat can be formed, the resin pellets first must be extruded into a flat sheet of appropriate size and thickness. This is where the technology takes a major departure from the rotomolding process, which is limited to a much more narrow selection of material types.

When such a sheet is created, the process allows two or three layers of differing but compatible materials to be formed into a single fused layer of even thickness. Typically, the sheet that will be used to make outdoor “weatherable” products will consist of at least two layers of different plastic material. The first or outer layer is frequently a modified acrylic. Acrylics have long been known to have outstanding UV resistance and are often used in glazing, car finishes, paints and even waxes. This layer will provide the sun protection, gloss, and exterior color of the product. Sometimes there is a second similar layer that exists for a special graphic effect, such as metallic or pearlesence. Next comes the “muscle” layer. The substrate will be much thicker and is often some form of high impact ABS. It can be the same color but is not necessarily so.

Here I would like to dispel a myth. I often hear remarks of the sort “Those kayaks are all made of the same stuff”. Except for the fact that yes, they are all made of plastic, nothing could be farther from the truth. Each resin manufacturer has unique patented formulas. They often manufacture varying grades of the same material that have different properties. The sheet can vary in the manufacturing process in many ways such as the ratio of thickness of differing layers, the amount of recycled content and so on. All these variables affect price and performance. Needless to say, the old adage still holds true for the most part: “you get what you pay for”.

Now the Process

Unlike fiberglass or rotomolded kayaks, thermoformed kayaks are typically formed over a mold rather than inside of one. With a female mold, the mold determines the surface quality, but with thermoforming the surface quality is already in the sheet and our job is not to mess it up. There is another reason for male molding. The sheet will stretch some as it forms. A male mold will see the greatest material thickness on the bottom of the hull where the most wear occurs. During the molding process itself, a sheet is clamped into a frame that holds it like a piece of glass in a window frame. The frame moves into an oven that heats the sheet to a high temperature, commonly between 350 and 400 degrees. At that temperature the sheet becomes quite rubbery and will stretch with ease. At this point the frame moves out of the oven to a position over a mold. The mold moves into the sheet until the edge seals against the hot plastic. At this time a vacuum is applied to the mold. This quite literally sucks the material down around it and into any fine detail on the mold itself. Once cooled in this position, the material now has a new shape and a kayak part is born. Remaining steps to an actual boat are trimming, rigging, assembly and detailing.

What are the essential differences? Thermoforming provides a product similar to the quality of fiberglass in appearance and performance, but at a lower cost. A wide variety of high performance materials are available that are expensive, but labor requirements are much lower than that of fiberglass composite kayaks. Thermoforming technology itself is not new, it has been around as long as plastics themselves. However the biggest changes are in equipment, process sophistication and the plastics themselves. Plastics used in thermoforming kayak are strong and they are easily repairable. Outer surfaces are harder than other plastics and even gel coat. This provides better abrasion resistance, no fuzz up, better UV resistance and more weight reduction. Other changes that have brought thermoform technology to the surface again are advancements in adhesives. Modern structural adhesives now regularly available have made possible the assembly of a variety of plastic parts with high structural integrity. Unfortunately, they still do not work well on polyethylene, but they do work well with the more expensive plastics used in thermoformed kayaks.

What is the downside? Fiberglass will probably have the edge for a while in overall longevity as will polyethylene in the extreme high impact world of whitewater. Nevertheless, modern thermoform materials offer great value and performance for the dollar spent on recreational and performance sea kayaks and with reasonable care will provide many many years of pleasurable use.

The future is bright too. Since Eddyline introduced its first thermoformed kayaks in 1996, at least five other companies have introduced one or more models, and the list is growing rapidly. We will continue to see significant advances in material and forming technology. We will also see more development of hybrid technology combining plastics and composites. Ultimately, these advances will continue to lower manufacturing costs and improve performance. Last but not least, all trimmed and unused material is 100% recyclable. Nothing need go into the land fill.