Before we prepare the product description, you can read the official text of the producer:

Better fabrics. Elite performance. The Trek-T takes it further. Made from Better Cotton Initiative (BCI) cotton, the Trek-T has reduced environmental impact – meaning it's better for the outdoors in almost every way. breathable polyester mesh at the back ventilates to optimize your run.
Brand:
On
Product code:
1ME10100553
Gender:
Material:
Front: 80% cotton (BCI), 16% recycled polyester, 4% elastane Back: 92% recycled polyester, 8% elastane
Determination:
Weight:
230 g

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