There are two CatBib sizes: Regular, and the Big Bib.
The best size for your cat depends not on how big the cat is but how aggressive. If in doubt, start with the Regular size.
The regular triangular-shaped size was tested by Murdoch University Biological Sciences Department and shown to stop 81% of cats from catching any birds, 45% of cats from catching small mammals, and 33% of cats from catching herpetofauna
One out of 5 cats may defeat the regular CatBib…for those more aggressive cats, the Big Bib may stop their bird catching. This larger size was tested by customers and works most of the time to stop even the most aggressive cats from catching birds.
In Australia and New Zealand, from the first 340 Big Bibs tried by cat owners only two owners reported failures. The Big Bib provides a good option for those really determined hunters on which the regular size has failed.
Both sizes are cat friendly and you cat can run, jump, climb trees and groom itself quite normally whilst wearing one. The Murdoch University research found that there were no welfare issues for cats wearing bibs. They just can't catch birds anymore!