Both puff pastry and phyllo dough utilize layering of dough. Puff pastry is created by incorporating butter into the dough. On the other hand, phyllo dough all by itself is virtually free of any fat. Rather the fat is added right before baking. Phyllo dough doesn't puff when it bakes—it crisps. Phyllo dough does not puff when during baking whereas puff pastry, as the name implies does puff during baking.