Thermal interface materials (TIMs) are used as an aid in transporting heat away from a circuit or electronic module. Composite materials are a popular research area for TIMs because they allow the desired properties from the individual constituents to be combined. The composite selected for this study uses carbon nanotubes (CNT) as the filler and an elastomeric polymer for the matrix, specifically a multiwalled carbon nanotube (MWCNT) / polydimethylsiloxane (PDMS) composite. Additionally, functionalization of the CNT may affect the composites’ thermal conductivity because of its effect on the CNT dispersion in the polymer matrix and its effect on the CNT-polymer interface. The objective of this study was to determine the effect CNT functionalization has on the effective thermal conductivity of a MWCNT/PDMS composite. The three functionalization’s used in this study are unfunctionalized, functionalized with a carboxyl group, and functionalized with a hydroxyl group. Secondary objectives were to develop the initial stages of a carbon-polymer composite database and to perform an uncertainty analysis on the stepped bar apparatus used in this study. The database is to be used for visualization of data found in literature to promote data driven research. The uncertainty analysis on the stepped bar apparatus is to qualify the instrument for thermal measurements in this study Initial results showed some increase in thermal properties of the composite, but there was little difference between the thermal conductivity of the three functionalization’s because of the high level of uncertainty used early on in this study. Later results showed an increase in mechanical properties of the composite which offset any thermal advantage with use as a TIM. A stronger composite means less compression under a similar load, resulting in a thicker TIM and higher resistance. However, the mechanical and thermal properties compound to show that -OH functionalized MWCNT present better properties for a TIM than unfunctionalized and -COOH functionalized; none show better results than the polymer by itself.