Deformulating low molecular weight and inorganic additives and fillers is relatively routine, but understanding the polymeric composition of a formulation is substantially harder. For composition analysis, more specialized techniques are required, such as Pyrolysis-gas chromatography-mass spectrometry (Py-GC-MS). In this case study, Py-GC-MS was used to examine two silicone adhesives. One adhesive reportedly had good adhesion quality while the second adhesive had poor adhesion quality. Testing revealed that the adhesives had two different siloxane structure types: linear and cyclic, likely influencing the bond properties.