No, not necessarily. Navy beans are small and cook nicely but you can use any beans you'd like. You can even use a mix of beans, like a 7-bean mix. Just remember to discard any seasoning packets that come with it because you will be using your own seasoning. 30 minutes is a nice average cook time for beans that are about the same size as a navy bean or smaller. If you want to use larger beans, your cooking time will increase. So for beans like cannellini or white kidney beans, you will want to add another 5-10 minutes. Note that some beans may be larger in size but thinner in thickness, they will have a slightly different cook time. You can always consult your pressure cooker manual for exact cook times.