Double pool floats can be foam filled or an inflatable one.
The foam filled ones have a core layer of soft foam, with an outer vinyl layer. These are thinner than inflatables and hence allow you to float really close to the water surface. Also, it will stay afloat even if the outer vinyl layer gets punctured.The caveat is that these are heavier and pricier. If you are short of storage space, then these might not be the best of choices.
Inflatables are easier to store and carry, inexpensive and available in hundreds of shapes and sizes. However, these will tear and spring a leak from time to time no matter what the manufacturer would like you to believe. Also, you need to invest in an air compressor pump, lest you wish to put your lungs to the test every time you wish to inflate it.