What is a midsole for?
The midsole is arguably the most crucial element of a running shoe, particularly in a shoe that’s designed for the purpose of transcending distance, as is the case with Mount to Coast’s range of ultra-focussed shoes for endurance training and racing.
A midsole has a number of critical functions:
- Cushioning and comfort – the midsole absorbs the shock of impact.
- Stability – the midsole has to be stable enough to provide a reliable platform for the runner.
- Energy return – athletes demand responsive shoes that help minimize their energy expenditure at a given pace.
- Durability – in addition to the first three points, a good midsole has to have a long lifespan to provide value to the athlete and minimize waste.
Mount to Coast incorporates a number of interesting technologies into our midsoles, chiefly ZeroSag.
What is ZeroSag?
ZeroSag is a revolutionary innovation in midsole tech. Co-developed by Mount to Coast and BASF, a leader in chemical innovation, this groundbreaking technology represents a new era in athletic footwear performance. At its core is Elastopan® polyurethane (PU), a material crafted through advanced polymerization of high-quality isocyanates and polyols. This outstandingly processable material combines the exceptional elasticity of traditional rubber with the robust strength of plastics. Widely used in industrial applications such as automotive suspension systems, it demonstrates unparalleled reliability and stability, even under extreme conditions. To a shoe designer, these are dream characteristics.
Properties of ZeroSag
The table below highlights ZeroSag's impressive physical properties, particularly its tensile strength, elongation, and compression set—a key metric for evaluating a material's resistance to permanent deformation under compression. This performance is assessed using a compression set test, conducted per established industry standards such as ISO-815 and ASTM-D395.
Compression Set Testing
Compression set testing measures the rebound characteristics of materials subjected to long-term compression at specified temperatures. Typically, these tests involve compressing the material to 50% of its original thickness, placing it in a constant temperature and humidity chamber (e.g., 45°C for 6 hours), and then allowing a 30-minute recovery period before measuring its height. The compression set is calculated using the formula:
Why ZeroSag Excels
The graph below illustrates a comparison of ZeroSag’s compression set against other midsole materials, revealing its superior resistance to deformation and exceptional durability. According to BASF, ZeroSag maintains consistent physical properties across various temperatures, ensuring unmatched performance and reliability.
Designed for Ultramarathons
These attributes make ZeroSag an ideal choice for long-duration activities, such as ultramarathons and multi-day races where a midsole’s durability, energy return and comfort are really pushed to the limits. Where it is integrated into Mount to Coast's running shoes, ZeroSag enhances the experience with its durability and stability. And combined with Mount to Coast’s unique Goflow design, it guides your stride while providing sustained support for longest runs – a perfect synergy.
