Heidi Klum has posed nude -- all for a good cause, of course.

The supermodel and "Project Runway" host, who turned 41 on Sunday, stripped down to promote a new campaign for the American Foundation for AIDS Research.

The foundation has a new tote bag for sale designed by Jean-Paul Gaultier to benefit AIDS research.

"Our longtime friend @HeidiKlum bears all for @amfar...to raise HIV/AIDS awareness," the foundation writes on Instagram.

The summery, nautical-inspired bag went on sale June 1 at Bloomingdale's, and 100 percent of the proceeds go to amfAR.