Koroyd™ is composed of masses of co-polymer tubes that are thermowelded together and shaped (in the case of helmets) into a honeycomb-like structure that can be integrated into helmet liners.

Upon impact, the Koroyd™ tubes collapse and, like EPS foam, slow and reduce the transmission of energy to the head. As used in helmet liners, Koroyd™ is a single-impact product. It’s currently seeing use in a few cycling helmets in tandem with EPS foam.


Zorbium ® was created in 2002 and is a proprietary open-cell foam that its inventors (a Cleveland-based company called Team Wendy) claim is rate sensitive. To wit, the foam is said to deform easily in a lesser, low-speed impact, yet firm up in a harder impact.

Zorbium ® is also said to regain it’s shape and protective qualities after a crash, making it suitable as a helmet liner in multi-impact helmets. While Zorbium ® was originally promoted as a material for winter sport, skateboarding and cycling helmets, it has largely been restricted to use in Team Wendy’s line of tactical (law enforcement and military) helmets.

Air (Bladders)

In the 1970s two helmet manufacturers, Schutt Sports and Riddell, introduced football helmets that contained inflatable, vinyl bladders. The idea was simple: once a player strapped on his/her helmet, they would attach a pump to an inflation port on the rear of the helmet shell and inflate the vinyl bladders; this would help provide an optimal fit and improve impact attenuation. For the same reasons, Bell incorporated air bladders into bicycle helmets in the 1990s.

Inflatable liner pads are widely used in football helmets today, though there is some debate regarding the efficacy of air bladders. In order for the technology to be effective, players must inflate bladders to optimal levels and maintain proper air pressures over time.


Pith is a spongy tissue commonly found within the stems of Aeschynomene aspera—a plant commonly found in marshy regions of Bangladesh, Bhutan, Cambodia, India, Indonesia, Malyasia, Nepal, Pakistan, Sri Lanka, Thailand, and Vietnam.

In the 1800s, Pith was used as a helmet liner material.

Thanks to its light weight, “Pith helmets” were popular amongst 19th century European colonizers operating in hot climates. It’s worth noting that not all pith helmets actually contained pith; some contained cork, which was readily available in Europe. Pith helmets were in active use until the 1940s.


While many people wouldn’t immediately think of metal as a primary helmet material, few other materials have been so extensively employed in helmets. Early metal helmets were designed for military use. Bronze helmets dating back to the fourth millennia BC have been unearthed in archeological digs. Ultimately, bronze, brass, iron and steel would all be employed to help soldiers deflect rocks, swords, hatchets, arrows and musket balls.

Naturally, there are downsides to wearing a metal bowl on your head. Poor ventilation, and excess weight are all disadvantages of the material. Compared to modern materials, metal’s ability to attenuate impacts is also lacking. By the 1700’s metal helmets had fallen out of favor as high-powered rounds from rifles could easily penetrate steel helmets.

Metal helmets, however, made a return with the outbreak of World War I. Though still ineffective at shielding their owners from rifle shots, steel helmets were then useful in protecting fighters from a new threat—artillery shrapnel and falling objects. While most armed forces no longer use metal-shelled helmets, it was only relatively recently that metal helmets were replaced with non-metal, composite models. The steel M1 helmet, for example, was worn by members of America’s armed forces until 1985.

These days, metal is rarely used in helmet shells and is largely relegated to the buckles and snaps that help secure some helmet straps.

Corrugated Fiber Board

Corrugated fiber-board consists of fluted or “corrugated” paper (often reinforced with fiber), that is either sandwiched between two sheets of paper product or adhered to a single sheet. To put a finer point on it, this is the material most “cardboard” packing boxes are made from. Corrugated paper products date back to the 1850s and were used in the construction of hats and, by the 1870s, the common cardboard box.

In recent years, a few small companies and inventors have experimented with employing interlocking rows of corrugated paper to make a sort of honeycomb helmet liner for cycling helmets. Much like a crushable EPS foam, the cardboard honeycomb is designed to collapse during an impact and reduce the amount of force transferred to the wearer’s head. The corrugated material is typically coated with an acrylic waterproofing agent to prevent it from absorbing sweat.

Most of the helmets employing this material have been of the experimental, prototype variety, but at least one brand has introduced a helmet that pairs traditional crushable foam liner material (EPS) with the fiber-board honeycomb and a thermoplastic shell.

While corrugated fiber-board is a relatively inexpensive product, labor costs associated with assembly of the interlaced honeycomb structure may well exceed the costs of manufacturing many of the crushable foam liners already popular on the market.


Most trees have an outer layer of cork bark. The cork oak, or Quercus suber, however possesses a much thicker band of cork than most tree species. This cork layer is composed of water-resistant cells that separate the outer bark from the delicate interior bark. The cork protects this species of oak from the fires, droughts and temperature fluctuations that are common Mediterranean countries such as Algeria, France, Italy, Morocco, Portugal and Spain.

Cork was used to pad helmets during the 1800s. You can think of cork as a precursor to the collapsible foam liners in modern helmets. Cork could be found in many “pith helmets” as a readily available substitute for the actual pith, a material primarily harvested from vascular plants native to Asia.

Cork is rarely incorporated in helmets today, though it does have a few interesting things going for it as a material. Cork is lightweight, rot resistant and impermeable to liquid, which is why it has been the preferred means of sealing wine bottles for more than 400 years now. That said, the labor costs alone (it must be removed from trees, boiled and shaped) make it an unlikely choice for helmet liners today.


Leather was likely the first material employed as a helmet shell. It essentially served as a second skin, reducing damage from edged weapons. Leather—even heavily padded leather—leaves much to be desired when it comes to impact attenuation. However, it is readily available, as well as comparatively affordable and easy to fabricate into a finished product (easier, that is, than smelting ore and casting or forging metals).

Metal replaced leather as the premier helmet shell material sometime during the fourth millennia BC and this remained true into the early 1700s. Leather helmets enjoyed a revival in military applications, however, from the mid 1700s until the early 20th century, when artillery shrapnel made metal a suitable choice for helmet shells again.

Leather helmets, however, did survive for quite a long time in sporting applications. The first (American) football helmets were constructed in the 1890s. Within a few years leather football helmets became de rigueur and continued to be until the early 1950s. Early motorsport helmets were also constructed of leather—usually with cotton or other organic materials sandwiched between leather layers to provide a degree of impact protection. In the world of cycling, padded leather “hairnet” style bike helmets were the norm well into the 1980s.