Twice baked potatoes can become sticky if the potatoes aren’t mashed while they’re still hot, or if they are overmixed. The science behind overmixing is simple: when the potatoes are cooked, they develop swollen starch cells. When the potatoes are mixed, the cells are ruptured and release starch. The more cells that are broken, the starchier and sticker the potatoes will become. For the fluffiest potatoes, mix as little as possible.