Question

what will happen if oil is used instead of water in hot water bags

Answer 1

As i think it will provide more heat

Answer 2

If oil is used instead of water in hot water bags the warmth will not remain as long as it would with the water.

The product of density and specific heat for oil is much smaller than that of water. This indicates that the degree of decline of the temperature of the hot liquid in the bag becomes greater in case of oil, So the hot bag becomes ineffective immediately as it declines to give essential warmth for a significant period of time.