The best type of knitting bag for a large project is the one that offers the highest volume for the main pocket of the bag. This doesn’t include the size of the pockets, which don’t hold skeins of yarn. Take a look at the volume of the interior of the bag to see what the true size is, then search for a bag that has a higher volume. This will allow you to keep multiple colors of yarn in the same bag or have multiple skeins of the same color for a larger project with only a few colors needed.