Nice question reader Dorrie! Perhaps you are a professional baker or pastry student, yes? Because “dry” butters aren’t products that the rest of us can easily get. As the name implies dry butters have a lower water content than most other butters, around 3-5% versus 12-17% for conventional store-bought butter. Why might they be an advantage in making laminated dough? Because while some water is essential if a laminated dough is going to rise (see the below post on the mechanics of puff pastry) too much water can actually undermine rising by moistening the dough sheets such that they get sticky and limp. In that case the steam in the dough can’t push them apart and/or keep them aloft. Is dry butter essential for a good puff pastry? No it certainly isn’t, though dry butters generally do deliver a higher rise and a crispier end product. Thanks, Dorrie!