The front part of an airfoil is called the “leading edge” (as it “leads” the airfoil through the air).

Two designs were tested for the construction of the HPH blades, the first and the more conventional was made of lightweight balsa,
joined together using either styrofoam or monokote, with a load-carrying spar in the middle. The winning design, however, was a
custom made leading edge made of lightweight but durable foam, using hot-wire cutting technique.

The leading edge shape is cut out of a foam block and it already features the shape of the main spar so they could be seamlessly attached.

Along the span, the leading edge contains several sections that are designed to carry the vertical as the leading edge foam piece is made to be as thin as possible.