Natural buffalo horn. Longlasting, no splintering, no mess, no chemical processing. The standard and jumbo sizes are hollow and open at one end, so we use them as natural 'kongs' and stuff them with wet food to serve part (or all!) of a meal! The mini size is usually open at both ends and completely hollow so makes a very easy 'kong', but we do also get completely solid ones sometimes which make brilliant 'just chews' so if you have a particular preference, let us know in the notes at the checkout and if we have the type you prefer, that's what we'll send! They freeze pretty well with wet food inside too!