Rice bags have gained popularity in the past ten years. It's main attribute is that the rice filler is readily available and is inexpensive. Usually white, long grained rice is used. Instant rice is hardly ever used.
Of course the size and shape of the heating pad that you need will depend on how you intend to use it the most. Some people have several sizes and shapes.
Like other types of microwavable heating pads possible uses are relieving aches and pains, keeping warm,warming the bed, check out
microwavable heating pad to view the many shapes. shapes and uses.
The bag cannot be washed with the rice in it. Therefore a cover is recommend. There tends to be a slight " dough" odor which some people my find a little offensive.
Rice bags can also be used as a cold pack see hot and cold therpy for uses