Plastic and rubber materials have many useful physical and mechanical properties, but it can be challenging to select the right material for a specific project. Shore hardness is an excellent measurement to help you determine material suitability.

Shore hardness measures the hardness of a material by determining its resistance to indentation. These resistance values can be found using a durometer, which measures the hardness of plastics, silicone, rubber, and other polymers and elastomers on a standardized scale to ensure that the material has the right amount of flexibility or hardness.

As a leading developer and manufacturer of liquid molding technology, Hapco has the in-depth knowledge and expertise to help you determine the perfect material for your application. With more than 50 years of experience, our ISO 9001 certified organization is dedicated to providing quality urethane and epoxy materials to meet your needs. We use the durometer hardness scale—also known as the Shore hardness scale—to help you determine the best molding materials for your project.

Shore Hardness Scale

The Shore hardness scale is an internationally accepted standard that quantifies the hardness of a material. It offers a comprehensive snapshot that makes it one of the most valuable plastics and rubber hardness scales available. The scale operates within a numeric range of 00 to 100, with 00 being the softest material and 100 being the hardest.

To measure different categories of materials, there are three main Shore hardness scales:

  • Shore 00 is typically used for soft and flexible materials such as gels, soft foams, and highly flexible rubbers.
  • Shore A measures flexible mold rubber materials. This range includes most rubbers from extremely soft and flexible up to hard rubbers with minimal flexibility. It also evaluates non-rubber plastics that are semi-rigid and somewhat flexible.
  • Shore D is reserved for testing hard and semi-rigid plastics and rubbers.

Shore Hardness Comparisons

Shore hardness scales offer easily quantified hardness levels. To illustrate, we can compare common objects and materials that exhibit similar hardness. Use the durometer chart below to help you narrow down your shore hardness requirements.

Shore 00

  • Marshmallow: 10 Shore 00
  • Gel Insole: 30 Shore 00

Shore A

  • Rubber Band: 20 Shore A
  • Mouse Pad: 30 Shore A
  • Inner Tube: 40 Shore A
  • Pencil Eraser: 50 Shore A
  • Tire Tread: 60 Shore A
  • Shoe Sole: 70 Shore A
  • Leather Belt: 80 Shore A
  • Phone Cord: 90 Shore A

Shore D

  • Textbook Cover: 40 Shore D
  • Golf Ball: 50 Shore D
  • Shopping Cart Wheel: 60 Shore D
  • Wooden Ruler: 70 Shore D
  • Computer Case: 80 Shore D
  • Bone: 90 Shore D

When to Consider Shore Hardness

Shore hardness is an important consideration for nearly every rubber or plastic component. While some applications require flexible rubber for seals and joint padding, others may require hardened materials that can withstand heavy loads and impacts.

Another important consideration is how easily you will be able to extract your original model from a rubber mold once it is cured. Although a harder material may seem ideal for these operations, the material can also be more brittle, making it difficult to remove from the mold after curing.

For example, a thin-walled component with delicate features, such as a miniature drone propeller, would work best with Shore 30A silicone rubber. Shore 30A hardness allows the manufacturer to easily remove the part from the mold without damaging thin and delicate parts. Extracting a product with a harder durometer reading would likely result in breakage.

Contact Hapco for Your Next Project

At Hapco, we are committed to producing quality rubber and plastic formulations and for a wide range of molding applications. We work closely with our customers to determine the perfect durometer hardness as well as other physical and mechanical characteristics for particular components and applications.

With more than 50 years of hands-on experience in the formulation and manufacture of rubber molding materials and mold manufacturing equipment, the experts at Hapco are uniquely suited to provide you with relevant advice on materials, equipment, and processes. Reach out to us today to learn how we can improve your molding operation, or request a quote for your next project.