Paper bags that will replace plastic t-shirt bags will cost substantially more to retailers.  Some estimate that the current charge of 5 cents per bag will be increased to as high as 15 cents per bag.  Retailers that have experimented with paper bags made from recycled fibres had to discontinue their use because of paper is considerably weaker resulting in bags ripping and the bottoms tearing apart.  The theory of using anything recycled is great for the environment.