What Kind of Foam Is Used in a Motorcycle Seat?
by Chris Gilliland
Motorcycle seats come in a different shapes and sizes, but their primary role is to provide a comfortable and stable perch for the rider. The typical motorcycle seat can be made in either a single piece or in layers of open-cell, polyurethene foam or closed-cell, polyethelene foam that is molded into the shape of the seat pan. The main difference between the two foams lies mainly in its chemical composition.
Foam Properties
A motorcycle seat's foam is selected by two properties: the foam's density and its firmness or Indentation Load Deflection. Density refers to the weight of the foam. The heavier the foam, the longer it will retain its shape over a period of time. Density is measured in pounds per cubic foot. A foam with a density of 1.2 lbs, for example, means that a 12 inch by 12 inch foam cube would weigh 1.2lbs. The firmness of the foam, the Indentation Load Deflection, denotes the foams ability to resist compression. Firmness is measured by pounds of force required to compress the foam using a rising scale, with lower numbers denoting a softer foam and firmer foams listed with higher numbers.
Open-cell Foam
As its name implies, open-cell foam is made of a framework of tiny broken cells. This allows air to freely enter into the cells, providing a soft cushioning effect. Open-cell polyurethane foams have the advantage of being very flexible and makes an excellent material for a seat's top cushioning layer. According to DIY Motorcycle Seat's website, a high-quality open-cell foam should have a density of 2 lbs and a 40 lbs. Indentation Load Deflection rating.
Closed-cell Foam
Closed-cell foams are similar to the open-cell variety, however, the cells that form the foam's structure are sealed. A special gas is used to expand the foam during manufacturing, which is sealed within each cell as the foam cures. This creates a much denser cushion, opposed to the softer, open-cell foam, and is an ideal material for a seat's base support layer. In some cases, a motorcycle seat may be composed entirely from closed-cell foam. This method is used frequently by racing motorcycles since the lightweight closed-cell foam provides superior grip to prevent the rider from sliding in extreme maneuvers.
Considerations
The foam used in motorcycle seat construction is normally made from the highest quality materials. However, open-cell foam is susceptible to water absorption. Tears or holes in the seat's cover can allow water to enter the seat and become trapped within the cushioning layers of open-cell foam. If left unattended, the open-cell foam can begin to deteriorate over time. Keeping a close eye on the seat cover's condition is the best way to prevent this from happening.
Modifying the Seat Foam
Motorcycles are designed to fit as wide of a variety of body styles and shapes. This translates into a seat that may not be as comfortable for one person than another. To help tailor the seat to your particular body, the seat's foam can be trimmed to better suit you. With the seat cover removed, the foam can be shaped with a sharp knife, sander or angle grinder using precise measurements. Alternatively, additional foam can be laid over the seat to increase padding as desired.
References
- "The Professional Motorcycle Repair Program"; Professional Career Development Institute; 1995
Writer Bio
An avid motorcyclist, Chris Gilliland has immersed himself into the two-wheeled world while balancing work life and raising three daughters. When he is not managing the parts department of a local, multi-line motorcycle dealership, Gilliland can often be found riding, writing or working on his motorcycle blog, Wingman's Garage.
