Ford is rolling out its inflatable rear seatbelts into more models starting next summer, adding the airbag-like restraints into the Ford Flex and into its Lincoln lineup.

Inflatable seat belts act much like air bags do in a crash, distributing the force of impact across a wider part of the passenger's body than traditional seat belts. They're also more comfortable to wear because they're covered in a softer webbing than regular seatbelt material, which could encourage back-seat passengers to buckle up.

Ford says the belts help reduce head, neck and chest injuries for rear seat passengers, who are often vulnerable passengers like children or the elderly.

The technology was first rolled out in the Ford Explorer that was introduced late last year. About 40% of Explorer buyers are opting for the technology, says Ford. About 87% opt for the rear view camera, and 40% opt for the blind spot information system.

The inflatable seat belts deploy when the car's sensors determine the vehicle has been in a collision. The tubular airbag inside the belt inflates with a cold compressed gas, which flows up a specially designed buckle. The airbags pop out like an accordion, expanding sideways across the passenger's body.

"It's a very simple and logical system, but it required extensive trial and error and testing over several years to prove out the technology and ensure precise, reliable performance in a crash situation," says Srini Sundararajan, safety technical leader for Ford Research and Innovation.

The belts cost $195 on the current Explorer, although they are not available on every version of the SUV.