With dry winter air comes flat hair. After sitting beneath a beanie and being beaten around by the wind for the past few months, your hair might be looking a little dull and lifeless right now. Thank goodness the beauty gods (okay, product developers) created volumizing shampoos. They give thin, flat, lifeless hair a shot of texture and thickness to make the hair appear healthier. Keep in mind one caveat, however: While volumizing shampoos add temporary life into hair, they can also contain ingredients that dry out your strands and overall deplete the health of your hair. That's why we consulted top celebrity hairstylists, including Ted Gibson, Glen Coco, Andrew Fitzsimons, Justine Marjan, and more for their best tips to get big, big hair.