By Rehan Iqbal
Non-slip or slip-resistant shoes prevent injuries by providing the wearer with extra traction, drastically reducing the chance of an injury from a fall.
People who work in the food services industry, construction, medical facilities, basically any environment where a wet or greasy floor can be a risk, should wear footwear that’s designed to prevent slips. They can be a real lifesaver for anyone who walks a lot, particularly in rain and snow.
The Science Behind Non-Slip Shoes
In the same way that the tires on a car are designed to provide maximum traction in wet weather, the soles of your shoes can do the same. Essentially, traction improves grip.
By increasing friction, non-slip shoes reduce the chance of losing your footing on a slippery surface. This is achieved by grooves on the outer sole of the shoe or work boot.
Scientists perform slip testing by measuring the coefficient of friction (COF) of the shoe. This is the ratio that exists between normal force and friction force.
The COF of Slip Resistant Shoes
Various tread patterns are used to increase friction between the shoe and the surface that you’re walking on. The groove orientation and its width are the most important factors affecting the efficacy of a slip-resistant shoe or boot. The materials used for the sole will also play a role.
The best non-slip shoes have a high COF value, and this is achieved in the following ways:
Slip Resistant Outsole Materials
To increase friction, as well as improve durability and comfort, a variety of materials are used to manufacture non-slip soles for shoes.
The material used can affect the price of a work shoe. It is, therefore, important to understand what materials are used and what benefits they provide.
Different working environments may have specific requirements. Consequently, there are several factors that you need to consider when comparing the materials used for the outer, inner, and mid sole of a non-slip safety shoe.
Before deciding a particular type of safety shoe, the following aspects should be carefully considered:
Also known by its abbreviation (PU), polyurethane has the advantage of being lightweight and comfortable. It has a relatively high resistance to most chemicals. PU offers good grip and can withstand a wide range of temperatures. Polyurethane has good anti-static properties.
There are several variations of polyurethane shoe soles, each with their own pros and cons:
Rubber is an extremely robust material with exceptionally good slip resistance. Pure rubber is not the best for very cold conditions. By using additives, like nitrile, temperature tolerance can be improved. As a result, rubber boot soles can withstand temperatures of -22 to 572°F (-30 to 300°C). Many consider rubber soles to be the ultimate material for most types of work shoes.
Rubber soles are one of the best options for workers in the petrochemical industry due to their resistance to hydrocarbons. It is also resistant to many chemicals and microbes.
While rubber has many redeeming qualities, it is heavy and causes fatigue. To mitigate the weight disadvantage, other materials, like PU or EVA can be used for the midsole.
Ethyl vinyl acetate is a soft and flexible foam material primarily used for the midsole of work boots and running shoes. It shares many of the qualities of rubber but is lighter and offers improved shock absorption.
It can withstand a wide range of temperatures, chemicals, oil, and fuel. EVA is often used to reduce the weight and improve the comfort of work boots with a non-slip rubber outer sole.
Thermoplastic rubber (TPR) is a synthetic rubber, sharing many of the properties of natural rubber. It is made from block polymers like Styrene-Butadiene-Styrene (SBS). The raw material is cheaper than natural rubber and is more easily processed using injection molding. As a result, TPR non-slip shoes are relatively inexpensive, making them very popular.
TPR is very durable and has a fairly good tolerance to extreme temperatures. It can handle a temperature range from -40°F to 248°F (-40°C to 120°C). It is also resistant to a wide variety of chemicals, including hydrocarbons, dilute acids, dilute alkalis, oil, and fuel.
Croslite is a trademark of the Crocs shoe company. It is a closed cell resin foam made from EVA. It is odor resistant and inhibits bacterial and fungal growth. As a result, it can be used in direct contact with the skin and is easy to clean.
Apart from its non-slip properties, Croslite is also extremely lightweight and UV resistant. It is also flexible and shock absorbent.
The Vibram shoe sole was invented by Italian mountaineer, Vitale Bramani, in 1937. While the deign was initially developed to provide improved traction and insulation for climbing and hiking in icy conditions, Vibram soles have become a popular choice for many work boot and outdoor footwear brands.
The outer sole is made from vulcanized rubber, with a PU midsole to improve shock absorption. Hexagonal lugs on the bottom of the sole improve grip. The sole also has wide channels that allow mud to pass through and aid self-cleaning.
The reinforced heel and toe make walking downhill easier, and the internal shank improves traction on uneven terrain. The design also provides good arch support. Vibram boots are often preferred by outdoor enthusiasts and people who work in particularly harsh environments where the terrain is uneven.
Innovative designs for tread patterns will greatly enhance the grip of a boot. The complex design of slip-resistant shoes allows liquids, like oil and water to be channeled away from the center to outer edges where it is easily expelled.
Generally, small tread patterns work better, with manufacturers differing in their opinions as to what design shape is better.
Numerous shapes and patterns are used to maximize grip:
How to Maximize Traction on a Slip-resistant Shoe
Generally, the greatest surface area is preferable to improve grip on a smooth or slippery surface. However, slip-resistant shoes are designed for various conditions.
In a job where water and oil pose a risk of slipping on a smooth surface, a work shoe must be good at channeling liquid away from the shoe. This requires a boot with many small patterns and grooves that force the water out of the sole.
Shoes designed to improve athletic performance have maximum traction by increasing the surface that makes contact with the surface and may not be the best in wet or icy conditions.
Outdoor slip-resistant shoes and boots tend to have large lugs that don’t have the best contact with the surface but improve grip when the ground is uneven or is made up of loose material like gravel or rocks. These boots are not the best for a smooth surface like ceramic tiles or smooth concrete.
Scientific innovations in the field of slip-resistant coatings for outsoles have revolutionized the footwear industry. The Kirigami coating is one of the most significant breakthroughs in slip-resistant outsole design.
Kirigami, named after the Japanese art of 3-dimensional paper-folding art, is a unique method of improving grip for shoes. A flexible material, made from plastic or metal, is covered with multiple triangular, square, or curved spikes. They follow the natural movement of the foot.
When the foot is flat, the spikes are retracted, maximizing the surface area of the outsole. As the foot moves, the spikes lift and increase grip on the area of the foot that is in contact with the ground. The coating can be applied to any type of shoe and improves safety on all slippery surfaces.
How Do You Know if Shoes Are Non-Slip?
By inspecting the outsole of a shoe or work boot, you can get a sense of how good they are in terms of slip-resistance. However, it is better to look for manufacturer certification that the shoe is slip-resistant.
A label on the tongue of the shoe and the packaging with the words “non-slip” or “slip-resistant” is a good assurance that the shoes are designed for slip resistance. This should be accompanied by an ATSM F3445 certification. This is the slip-resistance rating for work boots and is the best guarantee that footwear meets the necessary safety standards.