I have been on the lookout for high quality, eco mat bags that are affordable for 3 years! I love these ones, they have an organic cotton canvas outer fabric and sturdy cotton twill lining to create a yoga mat bag that will last.
Most modern fabrics are coated with polymer-based water-resistant coatings, which adds to microplastic pollution. Cotton canvas is not entirely 'waterproof', but it is water-resistant. The material swells slightly when wet, closing any gaps where water may seep through. The twill lining under the canvas acts as an extra barrier, keeping your belongings dry when you are caught in a rain shower.
You can even fit leggings and a top in the bag and there's an internal pocket for a phone and/or keys!