An internal valve (10, 10′ or 10″) and its methods of use for stabilizing and reinforcing inflatable objects are disclosed. The internal valve is a novel, simple modification to conventional check valves with the addition of a discharging means (14, 22 or 28)for external control. An internal supplemental chamber comprises one or more partitions that are secured, directly or by I-beams (40′), to main chamber's walls (40) of an inflatable object and stretched when the main chamber is inflated. With the internal valve as the passage to and from the main chamber, the enclosed or isolated supplemental chamber (30, 30′, 32, 34, 36 or 38) functions as a stabilizing or reinforcing component. A plurality of chambers 36 can form cylinder beams for an inflatable mattress.