As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
AIRCRAFT WOULD NOT PRESSURIZE AFTER TAKEOFF. FLIGHT RETURNED TO DTW AND LANDED WITHOUT INCIDENT. MAINTENANCE FOUND INSULATION BLANKET OBSTRUCTING OUTFLOW VALVE. REINSTALLED BLANKET. OPERATIONAL CHECK NORMAL. AIRCRAFT RETURNED TO SERVICE.