It's no secret that there are thousands of hair products on the market that promise to smooth hair while adding volume, but often they don't deliver. That's why fans are raving about this affordable $8 drugstore serum that Andie MacDowell used for her luscious hair at the Cannes Film Festival earlier this year. The L'Oreal Paris Elvive Plump Hair Serum features a lightweight texture that delivers instant hydration to your strands without weighing them down. The serum is designed to re-plump dry, dehydrated hair for up to 72 hours.