Ditto what Animal31 said. These plastic 'doll' noses come in all shapes and sizes from
fully shaped noses to just ovals, depending on the look you're going for. For larger puppets, I was also taught by Matt Ficner to use sculpey clay that you buy in craft stores. I'm no sculptor but, I've gotten pretty good results. To firm it up, you can bake it in your toaster oven per instructions. My sculpey noses thus far include these two characters. The second was painted with a gloss paint to give it that wet-nose shine: