With so many different types of durable rubber to choose from, pinpointing the perfect one for your project can prove itself a difficult task. While you probably have an idea of the color, thickness, and specific resistances needed in your application, you probably haven’t thought very much about the durometer hardness of the material. Durometer is a unique method of rating rubber hardness that was developed by Albert Shore in the 1920s. The system uses one of two particular scales indicated with a letter A or D, and assigns a corresponding number that indicates the hardness, flexibility, and resilience of rubber materials tested. To make sure you pick the perfect rubber for any project every time, you are going to need a good understanding of Shore’s durometer hardness scale.
The simplest and most important thing to remember about durometer hardness is that the higher the number rating is, the harder the rubber material is going to be. For example, soft rubber playground flooring typically has a durometer hardness around 40 Shore A, whereas heavy-duty industrial floors will have a rating closer to 70 or 80 Shore A. Both are effectively durable rubber materials, but the playground surfacing demonstrates a clearly softer and more forgiving surface than the stiff industrial flooring. But, when comparing a Shore A 60 durometer rubber with a 70 durometer, distinguishing the difference with the naked eye can be tricky! To understand the difference between similar hardness ratings, you need to understand how hardness is defined by Shore’s durometer scale.
Understanding Durometer Hardness
For the sake of the durometer scale, the rubber hardness refers to the material’s resistance to indentation. To determine the durometer hardness of a rubber material, force is consistently applied to a specific spot on the surface, and the depth of the resulting indentation is measured. The harder a material is, the more force will be needed in order to leave a lasting indent. This method easily demonstrates the resilience of rubber, allowing us to assign it an appropriate hardness rating. Though rubber materials with different durometer hardness ratings may look and sometimes even feel incredibly similar, the rating indicates a significant different in both performance and possible applications.
Durable rubber products, depending on their individual consistency, may have a durometer hardness as low as 10 or 20 Shore A all the way up to 100, but the most versatile and practical products will have a rubber hardness rating right in the middle. Rubbers with a durometer hardness between 40 and 70A are seen most commonly. This is because 40-70 durometer hardness ratings indicate a mid-range rubber hardness. Rubber materials in this range generally very durable and resilient, with excellent physical resistances. 60 durometer rubber in particular is a favorable choice because it can hold up against heavy impacts and abrasions without sacrificing its sturdy form. The thicker the rubber is, the stronger these qualities will make themselves known. Another aspect that makes this durometer hardness a popular choice is its pliability. General purpose rubber is typically made using 60 durometer rubber because while the material is stiff, it can still be flexed to an extent. This demonstration of the resilience of rubber makes it ideal for a job of nearly any kind, from industrial seals and gaskets to fitness flooring and protective covers.
While 60 durometer rubber is a great hardness for general purpose projects, specialized applications may find a better fit in something a little softer or harder—depending on their specific needs. Rubbers with a soft, low durometer hardness are better for lessening impacts and providing anti-fatigue comfort. This is why most rubber playground flooring features a durometer hardness in the 40-50A range. Lower mid-range rubbers are able to provide flexible safety cushioning without sacrificing the material’s tough and durable surface. This type of flooring uses the resilience of rubber to cushion impacts, providing a more comfortable surface for children to fall onto. Fall injuries cannot be avoided completely, but a rubber floor with a low durometer hardness can reduce the risk significantly. Some of these durable rubber floors are even safety-tested for falls up to six or seven feet so they can be used in schoolyards and public playgrounds with confidence.
While rubber materials on the higher end of the mid-range may not be as comfortable and cushioning, they feature a durometer hardness that is much better-suited for heavy-duty applications. Material with a rubber hardness of 70 Shore A will be stiff and rigid, with very little flexibility. These harder, less pliable rubber materials are favored in protective and industrial applications. This is because the durable rubber has such a strong resistance to indentation. It would take an incredible amount of force to damage a rubber with a durometer rating higher than 70. A material with a 70A durometer hardness is perfect for physically demanding jobs, as the rigid material can withstand constant abrasions and impacts without compromising its defined form. You can use rubber with a 70A durometer hardness as a protective barrier for sensitive surfaces. The tough rubber will absorb harmful impacts, abrasions, and vibrations to ensure they never reach the surface below.
Because there is such a broad spectrum of rubber hardness ratings, it can be overwhelming trying to pick out the perfect material for your application. Every job is different, and requires a specific kind of durable rubber. Understanding Shore’s durometer hardness scale can create a world of difference when picking out material, as the ratings will always tell you how hard, flexible, and resilient each rubber is. Remember that the higher the rating, the harder and less pliable the rubber material will be compared to elastomers with a lower durometer rating. It can be tempting to always reach for the general purpose 60 durometer rubber, but with this new knowledge and understanding of hardness ratings you can make the most informed decision each and every time.