Polyurethane Sole Systems as an Alternative to EVA for Slippers and Sports Footwear

EVA-Equivalent Polyurethane Slipper and Athletic Sole Systems Footwear and slipper users prioritize comfort and durability when making purchase decisions, selecting products that deliver these characteristics. Polyurethane system manufacturers and shoe producers also focus on these preferences in their development work. Flokser Kimya, through its EVA-equivalent slipper and sole systems, aims to combine these properties and address market demand. Slippers and athletic sole products manufactured from EVA (ethylene vinyl acetate) offer users lightweight properties and comfort through their soft structure. However, EVA's lower mechanical performance compared to polyurethane results in reduced service life, which prevents the standalone use of EVA. For this reason, manufacturers and users turn to polyurethanes with good mechanical properties but poorer comfort characteristics—higher density and stiffer materials compared to EVA. The fundamental properties these two different raw materials provide in the sector represent two opposite extremes. Soft slipper systems, one of Flokser Kimya's product groups that previously set market direction, have been well received by users, and this development has created different market needs. Drawing on experience gained from this product group, Flokser Kimya's Research and Development Center found a solution to this market demand by combining the two opposing properties derived from EVA and polyurethane into a polyurethane formulation now offered to the market. No equivalent of this developed polyurethane currently exists in the sector. EVA-equivalent polyurethane systems have been developed for use in both slipper and athletic sole applications. Standard polyurethane systems used in slipper production have a density of 250–300 kg/m³, with hardness in the range of 45–60 ShoreA. The developed EVA-equivalent slipper systems, instead of the 45–55 ShoreA hardness of standard slipper products, enable production of soft slippers with 20–25 ShoreA hardness that provide the user with comfort and cushioning at the same density. Due to this hardness level and superior walking properties within the mold compared to standard slippers, it enables production of closed slippers without requiring insoles and uppers. Additionally, in designs requiring insole applications, it is preferred over polyether polyol-based fuspet applications due to its softness. [caption id="attachment_131331" align="aligncenter"] Figure 1. Slipper without insole and upper[/caption] Figure 1. Slipper without insole and upper In athletic sole production, polyurethane systems used have a density of 350–450 kg/m³, with hardness ranging from 40–50 ShoreA. Additionally, in the flex test—one of the tests demonstrating product durability based on use—results are obtained in the range of 80,000–100,000 cycles at −5°C. The developed EVA-equivalent athletic sole product enables production at 280–350 kg/m³ density at the same hardness level while offering approximately 25% weight advantage compared to standard polyurethane systems. In the compression set test conducted according to ASTM D395 standard, which shows the shoe sole's ability to maintain its shape under applied load, EVA soles recover approximately 10% of their original form after compression, whereas our developed H-510 and H-466 products recover approximately 74% of their shape depending on the compression ratio. This value exceeds both EVA and standard polyurethane values. Additionally, our EVA-equivalent polyurethane athletic sole product undergoes 25% less relative volume loss in abrasion testing compared to EVA soles, providing superior wear resistance. [caption id="attachment_131334" align="aligncenter"] Figure 2. Compression set recovery comparison graph after compression[/caption]

Thus, with the developed EVA-equivalent polyurethane systems, we deliver economical slipper and athletic sole products to market that offer comfort to end users.

[caption id="attachment_131337" align="alignnone"] Figure 3. Low-density athletic sole[/caption] A comparison of our EVA-equivalent polyurethane system with standard slipper and sole characteristics is shown in Table 1.

Table 1. Performance of our EVA-equivalent slipper and sole products versus standard slipper and sole systems

[caption id="attachment_131357" align="aligncenter"] *Reaction and working conditions were determined through measurements using a low-pressure casting machine operating at 6000 rpm. *Test results for samples are provided following conditioning for 24 hours at 23±2°C and 50% relative humidity in accordance with TS EN 12222 standard.[/caption]

Dr. Serpil Yılmaztürk Güney R&D Director Flokser Kimya

Kerim Can Ünlü R&D Manager Flokser Kimya

Tibet Hüten R&D Researcher Flokser Kimya