An improved array of spring units. In a preferred embodiment, the spring units are composed of polyurethane which are blow molded such that a string of bellows-like springs are provided, with the axial ends of each spring being free for axial compression, while the sides of the springs are left attached to each other during the blow molding process. In another embodiment, the blow molded springs each include a vent hole which affects the dynamic cushioning properties of the springs. In another embodiment, extruded tubes of particular configurations are slotted at spaced-apart intervals such that independent spring units are provided, with the axial ends of each spring being free for axial compression. The array of spring units does not require a fabric covering as do strings of pocketed coils, but may be as easily handled, and may be connected in side-to-side abutting relationship to provide a mattress, cushion, or box spring inner construction.