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Water heating experiments were carried out on four different double exposure box-type solar cookers(DEBSCs) containing different heat storage materials (HSMs) (i.e. benzoic acid, stearic acid, palm olein and no HSM) when the base reflectors were opened and closed to solar radiation. The change in temperature of water and HSMs, water heating power, sensible heat efficiency, and the amount of energy stored by the HSMs were estimated. Using the base reflectors, a water temperature boost of 20 oCwas attained without any HSM, while, a boost of around 6-15°C was attained with HSM. Heating power was observed to be higher when the base reflectors were used; with a difference up to 112, 60, 172 and 35 W in the DEBSCs with no HSM, benzoic acid, stearic acid and palm olein respectively. Using a base reflector makes the DEBSCs attain higher SHE. The average energy stored by benzoic acid, stearic acid and palm olein in the DEBSCs without base reflectors were; 178, 461 and 110 kJ respectively, while with base reflectors, the energy stored was; 182, 503 and 245 kJ respectively. The presence and absence of the base reflectors affected the performance of the DEBSCs.