When developing high-performance footwear, choosing the right sole is more than a design decision — it’s a science. Every outsole and midsole material has specific performance characteristics that directly affect how a shoe feels, functions, and holds up over time.
In this guide, we’ll break down the essential metrics used to evaluate sole performance, helping designers, developers, and product managers make more informed decisions.
1. Cushioning
Cushioning refers to how well a midsole absorbs and disperses impact forces. It plays a vital role in reducing joint stress and improving comfort over time.
- Why it matters: Good cushioning helps reduce fatigue and protects the body from repeated impact.
- Measured by: Compression set, impact force reduction
- Typical scale: Basic to Maximum (e.g. Cu 2–6 in the ALCMY system)
2. Rebound (Energy Return)
This metric measures how much energy the midsole returns after compression. High rebound foams make footwear feel more responsive and help reduce effort during movement.
- Why it matters: A more “springy” feel can improve running economy and reduce fatigue.
- Measured by: Energy return percentage (%)
- Examples: ETPU (70%+ return), EVA (50–60%)
3. Durability
Durability in soles typically refers to how well they resist wear over time, especially under repeated stress or friction.
- Why it matters: A longer-lasting midsole or outsole means less breakdown, better performance, and a longer product lifecycle.
- Measured by: Abrasion resistance, fatigue life, flex cycle testing
4. Grip / Slip Resistance
For outsoles, grip is essential. It’s measured by how well the sole maintains traction across different surfaces — dry, wet, oily, or uneven.
- Why it matters: Safety, control, and performance rely on reliable traction.
- Measured by: Coefficient of friction (slip test), SR ratings (SRA, SRB, SRC)
5. Abrasion Resistance
Abrasion resistance evaluates how well an outsole holds up against surface wear caused by repeated contact.
- Why it matters: Protects the structure and performance of the sole, especially in demanding work or outdoor conditions.
- Measured by: Weight loss or wear over a set number of cycles
6. Flexibility
Flexibility determines how well the sole moves with the foot. Some applications require stiffness (for support), others need free movement.
- Why it matters: Affects comfort, energy transfer, and biomechanical performance.
- Measured by: Flex cycle tests (e.g. Ross Flex), bending resistance
7. Impact Attenuation
This refers to how much force is absorbed during heel strike or forefoot impact. It overlaps with cushioning but is often tested separately in lab conditions.
- Why it matters: Helps reduce injury risk and improves user comfort.
- Measured by: Peak impact force reduction in lab tests
8. Tensile Strength & Elongation at Break
Tensile strength measures how much force the midsole material can handle before tearing. Elongation measures how far it can stretch before failing.
- Why it matters: Indicates the toughness and elasticity of the foam.
- Typical benchmarks: 12 MPa tensile strength, 400%+ elongation for performance foams
9. Density
Foam density affects both the weight and performance of the midsole. Lower-density foams tend to be lighter but may have reduced durability or rebound.
- Why it matters: Balances comfort, performance, and weight.
- Typical values: 0.15 g/cm³ (lightweight) to 0.25 g/cm³ (dense)
10. Chemical and Temperature Resistance
Materials should retain their properties across different environmental conditions. This includes UV, oil, and solvent resistance, as well as temperature stability.
- Why it matters: Ensures consistent performance outdoors or in industrial environments.
- Tested by: Material exposure and performance retention across –20°C to +40°C
Why These Metrics Matter
Every footwear application — from safety boots to trail runners — has a different set of needs. A high-rebound running midsole might fail in a safety context, just as a stiff outsole might ruin the comfort of a casual sneaker.
By understanding these performance metrics, footwear professionals can:
- Make more informed material choices
- Create better products with targeted benefits
- Communicate more clearly with factories and suppliers
At ALCMY, these metrics are at the core of our design system. Our ALCMY rating system takes the most important midsole and outsole metrics — cushioning, rebound, durability, grip, abrasion, and flexibility — and translates them into a clear, consistent language of performance.
Want to learn more about how we apply these metrics in our product development? Explore our catalog or contact us to speak with our development team.
