Why does your top radiator get soft while the engine is running?

If the question is: why does your top radiator hose get soft while the engine is running? If that's what u want to know, it's because the thermostat in the engine opens to flow the coolant thru the motor to keep the operating temperature from getting to hot. It's stores water in the radiator which cools the water and the thermostat blocks it until a predetermined temp.