Can you buy the resin g-star use in their jeans to reapply to a pair that were washed?

No, G-Star's specific resin treatments for their jeans are proprietary and not available for purchase. Additionally, the application process requires specialized equipment and expertise to achieve the desired finish and durability. If your jeans have lost their original treatment after washing, it's best to consult a professional denim care service or consider using a denim refresh product designed for home use.