The mass of any object tells you how heavy it is. For example, if a water pump needs 1 minute to draw $$1 \, \mathrm{kg}$$ of water, it will need 2 minutes to draw out $$2 \, \mathrm{kg}$$ of water.
You have $$1 \, \mathrm{kg}$$ of Iron and $$1 \, \mathrm{kg}$$ of Cotton. Which is heavier?