Abstract: A cab to cap gap filler apparatus includes a top assembly which includes a top width that is greater than a gap width of a gap between a rear of a truck cab and a front of a truck bed cap. The top assembly is flexible along lines which are parallel to the top width, and the top assembly has a top length which is sufficiently long for the top assembly to cover horizontal and vertical portions of the gap between the rear of the cab and the front of the truck bed cap when the top assembly is flexed around horizontal and vertical portions of the gap. A flexible housing assembly is connected to a bottom side of the top assembly and includes a portion which has a housing width which is less than the top width, and a quantity of moldable solid particulate material is contained within the flexible housing assembly.