By Greg Waters, Director of Global Sales & Marketing at Griswold LLC

Griswold LLC manufacturers the majority of its Kushon® cellular rubber products using natural rubber as the polymer base. While so many of today’s foam materials are petroleum based, our natural rubber is sustainably harvested on plantations in Indonesia.  Unlike soy and corn based products, natural rubber does not divert food materials from either people or livestock.

Rubber was harvested initially in South America where it originated. The trees and seeds were highly protected.  However, British businessmen smuggled seeds out of the Amazon in the 1870s.  Those seeds were used to grow trees that generated hybrids well suited to growing in the British colonies of Southeast Asia.  By 1910, the bulk of global rubber production had shifted to Malaysia, Sri Lanka, and Singapore.

Natural rubber is produced from the sap of approximately 200 different plants.  The most productive source is the Para rubber tree, Hevea Brasilensis, which is indigenous to the Amazon.

Natural rubber is treated with sulfur and heat through a process known as vulcanization, which creates rubber with greater elasticity, strength and hardness. Charles Goodyear, in the 1830s, discovered a method that greatly improved the basic properties of natural rubber. Today, that process, vulcanization, gives our Kushon Sponge its amazing durability and makes natural rubber suitable for a wide variety of applications in areas such as automotive, industrial, footwear and die ejection markets.

Griswold’s tree-derived rubber is also eco-friendly. The trees are tapped in much the same manner that sap is collected for the production of maple syrup.  A rubber tree is capable of producing sap for about 12 years, after which the tree is replaced with a new sapling. The thin white liquid that flows from the tree is collected and shipped to a central facility where the rubber is strained to remove foreign materials, like leaves and sticks. The liquid is acidified, causing the sap to coagulate.  Once the coagulate is rolled into sheets and dried, it is sent to manufacturers to develop product components.

During production, we recycle waste for all of our natural rubber Kushon products.  At the facility, the excess material is ground into particles with a dust like consistency.  That ground product is then added to new batches of Kushon, becoming salable product and avoids being discarded in the landfill or the incinerator.

With a sustainable formulation and production process, we are able to provide our customers with tough and durable products in flexible formats for a broad range of constructions while still remaining environmentally conscious.

Griswold Versatility of Foam


The versatility of foam is best demonstrated by the sheer number of markets and applications where it is used to solve design challenges. It provides a great number of solutions related to environmental sealing, vibration management, impact absorption, spring force, etc. Foam likely appears in your life in your car, cell phone, footwear, kitchen appliances, sports equipment, and more. The list is virtually unlimited.

The appeal of foam is generally based upon some very basic properties including; compressibility, shapeability and durability.


The ability of foam to be tailored in thickness and then compressed allows it to fit into a wide variety spaces. When foam thickness and compressibility are combined with desirable stress strain behavior, the list of challenges solved grows:

  • Foam does an excellent job of helping to manage complex thickness tolerance stack-ups.
  • Top notch environmental sealing of dust, liquid and light can be attained.
  • The matrerial provides optimized spring force in polishing applications including: pads for semiconductors, and lenses for prescription glasses.
  • Foam can provide optimal energy management in something as heavy as high speed rail or as delicate as your high heel shoe.


One of foam’s principal benefits is its ability to be shaped (mostly in two dimensions). Foam can be cut into a virtually infinite number of shapes – a process called converting – with a wide variety of cutting techniques: steel rule die, clamshells, rotary die cutter, water jet, laser, etc. Many foams can be provided in rolls or sheets to allow for efficient converting.


Carefully selected foam allows for durable, long term performance across a broad range of applications. The most important factor is compression set, c-set, resistance. C-set is a measure of how well a material resists damage due to continuous or repetitive compression. The lower the c-set number, the more compression resistant the foam, and the longer the material will perform well in your application. It is easy to envision that in the applications mentioned foam will not perform well if it is easily squashed.

In short, foam materials provide exceptional versatility to the designer across a broad range of markets and applications.

Choosing the appropriate foam for military footwear involves many factors as different boots are designed for select areas of specialty, which can greatly differ between the Marines, Army, Navy, and Airforce.

Military footwear is unique in that it is designed for a specific walking/running/climbing surface ranging from wet smooth landscapes to cold, rocky ones. In years past, previous designs did not focus on performance or energy absorption — but rather on the nature of the material of construction. This approach changed around the time of the first Gulf War and into the early 2000s when the Army began to notice the number of soft tissue injuries to the foot caused by walking on rough terrain.

Today lower limb injuries remain a continual and serious issue for military personnel. Keeping these needs in mind, in more recent times the military changed the boot specification to one based on performance in shock attenuation. Shock attenuation during running is the process of absorbing impact energy due to the foot-ground collision, reducing shock wave amplitude between the foot and head.

Our Approach

Griswold understands many of the unique material needs that address shock attenuation and energy absorbance, and so we developed a foam that could support these performance requirements. Our enlighten-u® product has excellent compression-set resistance and shock-absorption properties making it an ideal material for military footwear. The foam is also optimal for overcoming common wear-and-tear challenges. Based on its durability, it offers strong cushioning properties that wouldn’t physically wear away easily and provides better value than most closed-cell neoprene products.

Today, hundreds of thousands of military men and women are counting on Griswold materials to contribute not only to their boot comfort but also on the absorption of energy that can prevent them from receiving foot and leg injuries. We salute our troops for the sacrifices they make every day to protect our country and are honored to support them every step of the way.