Thermoplastic membranes have a different chemical composition from thermoset, which means that they don't necessarily have to be bound to the same type of material. They're welded shut and can contain fire retardants and materials to absorb ultraviolet light.
According to manufacturers, this type of roof is a good choice for restaurants and businesses that push oils out through ventilation systems because the membranes are highly resistant to oils, animal fats and bacterial growth. The membranes can also be installed over older types of roofs when a full tear-down isn't practical.
Typically, these rolls of plastic come in the cool colors gray or white, and that slick single surface improves the roof's ability to reflect light.