Hydrogen is the most abundant element in the universe and is 14 times lighter than air, making it the lightest atom on Earth. Hydrogen has two main characteristics: it is invisible and odorless. Hydrogen emits no CO₂ while burning, and it can be produced 100% from green electricity. Hydrogen can be stored as a gas under pressure, typically at 350 bar or 700 bar, or as a liquid when cooled down to -253°C.