The Hubble Air can be used as a side-sleeper when your little one is very young, or as a proper crib as they get older by simply raising or lowering the side as required. Each side of the crib can be height-adjusted separatly if your little one suffers from reflux. Otherwise, you can leave one side off, adjusting the crib to the height of your mattress and sleep side by side safely without the risk of injury. The crib comes with a soft foam mattress which is breathable- between that and the base, your little one can be kept nice and cool, helping you to regulate their temperature better. Both sides of the crib have mesh so you can keep a close eye on your child as they doze. A hydrophilic cotton sheet is included to keep the mattress covered nicely, this can be machine washed for your convenience. If you're on your travels, no need to worry- the Hubble Air can come with you! It folds down easily and compactly, and even comes with a transport bag so you can bring it along by the handy s