Physical Properties of EVA

The physical performance indicators of EVA (ethylene-vinyl acetate copolymer) generally include the following aspects: hardness, specific gravity, elongation, tensile strength, tear strength, compression set, and elasticity. Each indicator has its specific testing methods and application scenarios, detailed as follows:

1. Hardness:
Hardness refers to the material's resistance to deformation, i.e., the softness or hardness of the product, usually measured using a Shore durometer. The hardness range of EVA foam materials is quite wide, from over 10 degrees to more than 80 degrees. This indicator is particularly important for applications like insoles and cushioning materials. Different hardness levels of EVA products are suitable for different usage needs. For example, shoe soles generally require higher hardness, while inner lining materials may need lower hardness to enhance comfort.

2. Specific Gravity:
Specific gravity, also known as density, is the ratio of the material's mass to its volume. While many people can conduct preliminary measurements using simple tools, in a professional environment, a microcomputer density balance is typically used for accurate measurement. Specific gravity is a key factor in balancing lightness and strength of materials, crucial for products like sports shoes and protective gear that require both lightness and strength.

3. Elongation:
Elongation refers to the elongation at break. During testing, the EVA foam product is made into a specific size (e.g., 60*10*5mm), and then a tensile testing machine is used to stretch it at a constant speed. The length at break divided by the original length is the elongation. Elongation reflects the toughness and extensibility of the material; a higher elongation means the material can be stretched longer before breaking.

4. Tensile Strength:
Tensile strength is the maximum load the material can withstand when it breaks, usually tested simultaneously with elongation. It is an indicator of the material's resistance to tensile force. Higher tensile strength indicates that the material is less likely to break during use, suitable for products with high tensile strength requirements, such as around the eyelets of sports shoes.

5. Tear Strength:
Tear strength is the material's resistance to tearing. The test method involves cutting a small notch in an EVA sheet, fixing both sides of the notch in the two grips of a tensile testing machine, and then pulling. The load endured is the tear strength. High tear strength means the material is less likely to tear during actual use, which is important for products requiring high durability, such as protective pads and packaging materials.

6. Compression Set:
Compression set (sometimes simply referred to as compression or compression deformation) is the degree of permanent deformation a material undergoes under compressive stress. The test involves making the EVA into specified discs, placing them in a compression device, adjusting to the required parameters, and then putting them in an aging machine for several hours. Finally, the disc thickness is measured, and the value is calculated through several coefficients. Lower compression set indicates that the material can maintain its original shape during long-term use, suitable for products requiring shape stability, such as insoles and gaskets.

7. Elasticity:
Elasticity is the material's ability to return to its original shape after deformation, sometimes referred to as rebound. Some brands further divide elasticity into two parts: cushioning and resilience. Cushioning refers to the material's ability to absorb impact energy, while resilience is the material's ability to quickly recover after absorbing energy. This performance is especially important in sports shoes, shock-absorbing pads, and sports equipment, where good elasticity provides comfort and effective protection.

Through these detailed physical performance tests, we can comprehensively understand the characteristics of EVA materials and select the appropriate EVA materials according to different application needs, ensuring the performance and quality of the final products.