I use a brand called 'Suet to go', from Pets at Home. The ball has a greasy, soft feel to it, making it a bit messy to deal with, but the birds seem to love it! It is not hard and dry like most you buy; it has some 'give' to it, just like home-made ones. I have also bought suet to make my own, with dried fruit, bird peanuts and cheese in it - they didn't last long either!