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• Experimental investigation of the lateral coupling in rectangular elastomeric isolators. • Three types of bidirectional loading were considered using a 6DOF apparatus. • An analytical model was derived and validated for the force-displacement relationship. • Conclusions based on the lateral stiffness, damping, and residual displacement. Elastomers are ideal for application as base isolators due to their ability to accommodate large recoverable strains. The formation of a composite with reinforcement, either steel or fibers, takes advantage of the near incompressibility of the elastomer to enhance the vertical and bending properties of the bearing. Although the conceptual design of a fiber-reinforced and steel-reinforced elastomeric bearing is similar, the lack of flexural rigidity of the fiber reinforcement results in unique performance characteristics, especially in the lateral direction. In this paper, an experimental program is conducted to evaluate the effect of lateral coupling in rectangular unbonded fiber-reinforced elastomeric isolators (UFREIs). An apparatus with six degrees of freedom was used to apply a vertical load with simultaneous displacement in both primary lateral directions, whereas previous experimental programs are mostly based on a two degree of freedom analysis (vertical and lateral). The UFREI specimen was subjected to cyclic lateral displacements including tests with initial lateral offsets in the secondary lateral direction, in directions angled off the principal lateral axis, and in a circular motion. This experimental program is the first to investigate lateral coupling in rectangular UFREIs. A comparison was conducted based on the effective lateral stiffness, equivalent viscous damping, and energy dissipation characteristics. The considered rectangular UFREIs were found to exhibit lateral coupling but the degree of coupling and the impact on the structural performance under bidirectional loading require further investigation. Residual displacement was observed in the experimental program and is discussed in depth. Also, a theoretical equation is derived to calculate the lateral stiffness based on the angle of loading and lateral displacement. Theoretical values are compared with experimental results to verify the equation. [ABSTRACT FROM AUTHOR]