If your pipe stem will except filters you first need to know the size you need. Most filters are either 6mm or 9mm. Once you know that any online pipe and tobacco store sells them. The most popular I would say are Dr. Grabow and Medico. If you want balsa wood filters Savenellie sells both sizes but there are many others. Dunhill, big Ben, white Elephant and as mentioned above Nording keystones which is what I use. They work great. You just pour 10 or so in the bowl then place your tobacco. You can also add more of them which makes the bowl size smaller so if you want to smoke a certain pipe but it has a large bowl and you don't want to smoke that much they take up space at the bottom so you use less tobacco thus a shorter smoke.