Years ago, my cockatoo started self-mutilating. Before knowing about BirdSupplies, my bird had to wear hard plastic "cones"...Neither I nor my bird was happy about this! My vet told us about BirdSupplies and suggested trying a soft collar. I tried a couple different types of collars that BirdSupplies offered, before settling on the Fringy Cone Bird Collar that works great!
Since my cockatoo tries to bite his feet and his wings, I suggest going with one size larger than the size chart recommends (the size chart recommends a medium; however, I purchase a large). Cockatoos are very smart and teach themselves sneaky ways to get to the areas they want to mutilate; but the larger size collar helps prevent this. The only problem with the larger size is that the neck hole is too large for my bird. My suggestion to BirdSupplies is to make the neck hole smaller, but allow the customer to trim it to customize the hole size as needed.