Cost is one of the major factors to be considered when choosing a thermal insulator. Design engineers continuously strive to provide the best at the lowest possible cost. In the tropics climatic conditions are essentially hot and humid and a cause for daily discomfort. To some extent, air-conditioning of buildings has solved this problem. The major deterrent to air-conditioning is the exorbitant cost of imported thermal insulation materials. This has prompted a search for local, low-cost but effective thermal insulation for buildings. Coconut fiber is available at minimal cost from the copra industry in Trinidad, as it is a waste product from the coconut. The viability of using coconut fiber as building thermal insulation was explored by conducting thermal conductivity tests on 200 mm × 400 mm × 60 mm thick slab-like specimens. The test equipment used was a locally designed constant temperature hot box apparatus. This apparatus was designed to test slab-like specimens under steady-state conditions. The reliability if this experimental set up was checked using Gypsum Plaster. The thermal conductivity test results for coconut fiber over the density range 30 kg/m3 to 115 kg/m3 showed the characteristic hooked shape graph for fibrous material. For the 60 mm thick specimens at a mean temperature of 39 °C, a minimum thermal conductivity of 0.058 W/mK occurred at an optimum density of 85 kg/m3. The thermal conductivity of commonly used industrial insulators, namely loose-fill expanded vermiculite, cellular glass and blanket fiber glass, at a mean temperature of 38 °C are 0.066 W/mK, 0.061 W/mK and 0.052 W/mK respectively . When compared, these results show that air dried coconut fiber has far reaching potential for use as an effective building thermal insulation.