In this first part of our new series exploring what makes safety shoes safe, we turn our attention to another essential part of protective footwear – the sole.
There are many elements that go into making safety footwear, and they all play their part in offering protection against different workplace hazards. In an earlier blog, we looked at the different types of toecap protection and compared the merits of aluminium, steel and composite toecaps in safety boots and shoes.
Sole composition
The soles of safety boots, shoes and trainers are made up of three parts: the insole, the outsole and the midsole.
The outsole
The outsole is the part of the shoe, boot or trainer that comes into contact with the ground when you walk. Outsoles are normally dual density and mostly made from polyurethane (PU), thermoplastic polyurethane (TPU), ethylene-vinyl acetate (EVA) or rubber (nitrile rubber). Each material has benefits in different environments: they differ in terms of slip resistance, comfort, durability and level of protection from heat or chemicals. Wearers should choose the material which offers the best protection for their working environment.
Dual density vs single/mono density
Dual density soles are made up of two layers, the most common being two layers of PU: a softer, thicker layer on the inside for comfort, and a thinner, harder layer on the outside for durability and grip. Mono density soles – with a single layer of PU – are lighter weight but must by necessity prioritise the harder compound layer, meaning they may be less comfortable to wear and will certainly be less durable especially in heavy use applications.
The insole
Made from pulp fibres, leather or non-woven materials, the insole is the part of a shoe that comes into contact with the wearer’s foot. Often made with a cushioning material to aid shock absorption and provide extra comfort to the wearer, its primary functions are to ensure contact resistance and remove moisture, enabling the footwear to dry quickly. Insoles can provide shock absorption at the heel or at the front of the foot, depending on requirements. Removable insoles may also provide support for the arch of the foot, but care should be taken when selecting one as it may interfere with the protective properties of the shoe. This is the case when removable insoles are added to ESD or antistatic shoes.
The midsole
Protective midsoles, otherwise known as penetration-resistant midsoles, are made from either steel or composite textiles and are designed to protect wearers from injuries where there is a risk of stepping on a sharp object such as a nail. Steel midsoles normally sit within the outsole and composite midsoles sit between the outsole and the insole. They offer a similar level of protection against penetration by sharp objects, however as steel midsoles are completely embedded within the outsole construction, small areas around the edges of the sole remain unprotected. Due to the properties of metal, they will conduct cold, heat and electricity, which may make them unsuitable for wear in certain environments, including where workers must pass through metal detectors.
Textile inserts are significantly lighter, more flexible and more comfortable. They are hard-wearing, do not conduct electricity, and resist extreme heat and cold.
When purchasing steel midsoles, wearers should ensure they are made from stainless steel, which is resistant to corrosion, rather than coated carbon steel, which could become weakened by corrosion over time. As with all safety footwear, you should always buy from a trusted supplier.
At iSB Group, we are experts in safety workwear of all kinds, including footwear. Browse our range of protective footwear, including safety boots, safety shoes and safety trainers. Our experts are on hand to answer any questions you may have. Give us a call on 0121 749 4433 or email us.