An internal tensioning structure for use in an inflatable product fulfills the basic function of maintaining two adjacent inflatable surfaces in a desired geometric arrangement when the inflatable product is pressurized. The tensioning structure is formed by connecting a pair of plastic strips sheets via spaced-apart strands, such as strings or wires. When pulled taut, the strands provide a high tensile strength between the two opposed plastic strips. At the same time, the plastic strips facilitate a strong, long-lasting weld between the tensioning structure and the inflatable product.