The suit for A-12 and SR-71 pilots. From the CIA’s Breaking Through Technology page:
Two Lockheed subcontractors, the David Clark Company and the Firewel Corporation, developed a full-pressure suit and oxygen supply system based on ones created for pilots of the X-15 rocket aircraft. The aluminized suit and breathing apparatus would protect the pilot from heat radiated from the 400 degree F. windshield and the effects of depressurization and extreme cold encountered during a high-altitude bail-out. The S‑901 suits were custom-made and cost $30,000 in the mid-1960s.