(as) light as air
Exceptionally light in weight. The material in the coat is durable and waterproof, but feels as light as air. Don't worry, the box is big but it's light as air.
(as) light as ˈair/a ˈfeather
weighing very little; very light: I love this jacket — it’s really warm but it’s as light as a feather.Her sponge cakes are as light as air. OPPOSITE: weigh (half) a ton