19mm heater EPDM hose is a flexible hose that is typically used in automotive applications as a heater hose. EPDM stands for ethylene propylene diene monomer, which is a type of synthetic rubber that is commonly used in automotive hoses because it is resistant to heat, ozone, and chemicals. The 19mm inner diameter of the hose makes it suitable for use in vehicles with a standard heater system. EPDM hoses are also commonly used in industrial and residential plumbing applications because of their durability and resistance to chemicals.