A restraint system (10) for helping to protect an occupant (60) of a vehicle (20) having a roof (32) and a cabin (40) with a seat (50) for the occupant (60) includes an airbag (70) having a stored condition within the roof (32) and being inflatable to a deployed condition extending into the cabin (40) and aligned with the seat (50). First and second tethers (110, 120) each have a first end (112, 122) connected to the airbag and a second end (114, 124). A first retractor (140) is connected to the vehicle (20) and to the second end (114) of the first tether (110). A second retractor (150) is connected to the vehicle (20) and to the second end (124) of the second tether (120). The first and second retractors (140, 150) control the length of each of the first and second tethers (110, 120) when the airbag (60) is in the deployed condition.