<p>The current work addresses the challenge of elucidating the performance of fluoroelastomers within the HMX (octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine) based polymer-bonded explosives (PBXs). To simulate the confined interface in PBXs, bilayer films of F2314/HMX and F2311/HMX were designed. Neutron reflectivity (NR), nanoindentation, and X-ray reflectivity (XRR) were employed to examine the layer thickness, interface characteristics, diffusion behavior, and surface morphology of the bilayers. NR measurements revealed interface thicknesses of 45 Å and 98 Å for F2314/HMX and F2311/HMX, respectively, indicating deeper penetration of F2311 into the HMX matrix. NR also suggested a denser polymer network with a higher scattering length density (SLD) near the HMX interface for both fluoroelastomers, while the bound layer of F2311 was notably thicker. Nanoindentation cross-checks and confirms the presence of a bound layer, highlighting the differences in stiffness and diffusion ability between the two polymers. The consistency between the NR and nanoindentation results suggests that F2311 demonstrates better flexibility and elasticity, whereas F2314 is stiffer and more plastic. Accordingly, the structures and performances of different fluoroelastomers at the HMX interface are discussed, which can provide valuable insights into the selection of binders for PBX formulations tailored to specific applications.</p>