The Global Recycled Standard is a voluntary recycling standard that covers not only the share of recycled fibres, but also additional criteria such as social and environmental aspects. Harmful chemicals are also not allowed. That means you can be sure the recycled content is safe and traceable all the way from the recycler to the final product.
By the way, only products made from at least 50% recycled materials are allowed to use the GRS logo. You can find out more about the recycled fibres used at ARMEDANGELS here.