water bottles, containing water are to just maintain the warmth, have you ever noticed after you make a hot coffee, how long it stays warm

if you just warm the air in the incubator, whenever you open it, you let out all the warmth and then it takes awhile for it to warm back up. With the water bottles, you can open the incubator take a peak and close it back up and the warm water bottles will get your incubator back to that warm temp. fast.