PETZL - Replacement Foam Helmets, Vertex COMPATIBILITY: These foam pads are compatible with Petzl's VERTEX and ALVEO helmets. ADAPTABLE: This standard replacement foam includes a regular foam pad for most head sizes and a thicker foam pad for smaller head sizes. EASY: This replacement foam is easy to maintain. LIGHTWEIGHT: Weighs 15 grams. OPTIONS: Choose the corresponding foam for either the VERTEX or ALVEO helmet.