The integrated collector-storage solar water heaters are less expensive and can offer the best alternative for domestic applications particularly to small families to meet hot water requirements. The top heat losses of such solar water heaters are quite high during the night and the temperature of stored hot water is considerably reduced unless covered with extra insulating cover in the evening which is a cumbersome job. The transparent insulation material widely used in Europe for space heating can also minimize top heat losses, if used in such solar water heaters. For this purpose, two units of solar collector cum storage water heaters have been designed to study the relative effect of TI for retaining solar heated hot water for a night duration. Both units were identical in all respects except one of them was covered with TIM. The theoretical exercise was carried out to evaluate design parameters of ISC which revealed total heat loss factor (U-L) 1.03 W/m(2) K with TIM glazed against 7.06 W/m(2) K with glass glazed. The TIM glazed has been found to be quite effective as compared to glass glazed SWH and yielded hot water at higher temperature by 8.5 to 9.5 degreesC the next morning. The storage efficiency of such solar water heaters has been found to be 39.8% with TIM glazed as compared to 15.1% without TIM. The TIM glazing means not having to cover the ISC solar water heater with a separate insulator cover in the evening and thus makes its operation much simpler. (C) 2001 Elsevier Science Ltd. All rights reserved.