Backer rods are made of flexible foam and are available in many lengths & diameters. They can be inserted in garage slab contraction & expansion joints or concrete cracks to reduce the consumption of the sealant, which is expensive. Backer rods also have following other benefits: * Reducing the effective joint depth & sealant thickness * Increasing sealant elasticity * Increasing contact area between sealant & joint by creating an hour-glass shape * Making it easier to clean out the joint later, if required