Hot Water Bag This hot water bottles are made with high quality, odourless rubber. These hot water bottles are used to provide warmth, typically whilst in bed. They are also used for the application of heat to a specific part of the body. Used as a natural body warmer and also for heat therapy treatment. Useful in case of - joint pains, muscular cramps, menstrual pains, muscle pull, stomach and back aches, arthritic and rheumatic pains, bed warmer, sports aches and pains, soothing children and elders â¢ Hot water bottle is designed to be partially filled. â¢ Hot water bottle is made from natural rubber. â¢ When filling hot water bottle, do not use boiling water and fill to a maximum two-thirds capacity or less. â¢ Two litre hot water bottle.