Although the pattern for these bowls is titled "Felted Nesting Bowls", it would be more accurate to descibe them as fulled nesting bowls (12 of 50). Fulling refers to the process by which a woven or knitted item is shrunk by subjecting the item to moisture, heat, pressure and friction, while felting refers to the process of meshing unwoven fibers to create a dense material by subjecting the mass of fibers to moisture, heat, pressure and friction. 
I used two different brands of 100% wool yarn - Paton's Classic in a burnt orange colorway and Lion Wool in a cadet blue colorway. The large and small vessels were knitted with Paton's Classic while the medium and extra small vessels were made with Lion wool. After fulling, the large and medium bowls were the same size...and the small and extra small were also similar in dimensions. Obviously, different wools full differently. I prefer the end products that were knitted with Paton's Classic and will probably stick with this brand for future fulling experiments. This was my first attempt at fulling, but I'm pretty pleased with the results!