Take your KLIM Ai-1 Vest to another level of protection with the D3O® Level 2 upgrade backpad. This backpad is highly ventilated and flexible, offering the highest and most reliable level of protection for the KLIM Ai-1 Vest.Size SM Ai-1 Vest use SM backpad. Size MD Ai-1 Vest use MD backpad. Size LG-3X Ai-1 Vest use LG backpad.