These brands make eco-friendly jeans from relatively more earth-minded materials such as organic cotton (which uses less water and zero synthetic pesticides compared to conventional cotton), surplus or deadstock fabric (unused fabric that would otherwise be tossed out), or up-cycled textiles (fabric re-constructed from trashed clothes). They also are more mindful of their manufacturing processes, minimizing the use of toxic dyes and chemicals while maximizing water and energy efficiency where possible.
Source: https://consciousfashion.co/guides/9-sustainable-denim-brands-eco-friendly-jeans