This paper focuses on the characteristics of gap fillers and how they impact a printed circuit board (PCB) including compression characteristics of various types of gap fillers, from standard viscoelastic materials, to putties, to form-in-place. PCBs are very flexible and deform quite easily; how deflection impacts the overall compression of the gap filler will be addressed. Finally, the paper will offer suggestions for managing the stress created when implementing a gap filler onto a PCB electronic assembly.