Composites comprising of polycrystalline triglycine sulphate (TGS) or its deuterated analog (DTGS) in powder form dispersed in polyurethane (PU) are synthesized for pyroelectric sensor applications. TGS and DTGS have high pyroelectric coefficients, but are susceptible to humidity, and PU is inherently electroactive. So composites made of TGS or DTGS dispersed in PU can be expected to have high pyroelectric coefficient as well as immunity to humidity. Composites with inclusion volume fraction between 0 and 0.25 are prepared, and their dielectric, pyroelectric, and thermal properties measured. In general, deuteration leads to decrease in dielectric constant and specific heat, but increase in thermal conductivity. The pyroelectric coefficient and figures of merit get enhanced significantly with deuteration as well as inclusion volume fraction. Comparison with similar composites shows that these samples have the highest values for figures of merit, indicating their potential use as thermal/infrared detectors that are immune to humidity.