The enormous loss of heat from high temperature equipment like boilers, furnaces, kilns and incinerators necessitates the use of fireclay as lagging material for minimizing the heat transfer from these systems to the surrounding. This paper presents the thermal characterization and application of fireclay samples developed from Abeokuta North Local Government Area of Ogun state in Nigeria. The clay samples were excavated from two clay deposit sites namely; Idi-Ori (sample A) and Eruku (sample B), they were processed into powdered form and pressed into shape to determine their chemical composition and thermal properties vis-a-viz refractoriness, thermal shock resistance, thermal conductivity and specific heat capacity. The chemical composition reveals 30% and 33.2% alumina for sample A and B respectively. The result of thermal shock resistance was over 25 cycles for both samples. Also the determination of the refractoriness (melting temperature) reveals 1512oC for sample A and 1550oC for sample B, the specific heat capacity of sample A is 1,315.4 J/kgoK while that of sample B is 819.77 J/kgoK. Finally, the thermal conductivity of 0.1272 (W/mK) and 0.1441 (W/mK) were determined for sample A and B respectively. The Performance test of the refractory bricks developed from the clay was carried out using an incinerator operating at 706oC, heat minimization of 654oC (from 706oC to 52oC) was recorded from the test compared to fibre glass that produced 640oC  (from 706oC to 66oC)