A company has made a new material called ‘Wellwarm’. They want to use ‘Wellwarm’ to make
(a) A scientist tested ‘Wellwarm’ to see how well it insulated a beaker of hot water.
She tested ‘Wellwarm’ and three other materials as shown below.
material A material B material C material D
She wrapped each beaker in a different material.
She recorded the temperature at the start and 20 minutes later.
(i) What was the independent variable that the scientist changed?