All those bubbles act as insulation. They are little pockets of air, warmed by the incubator and they retain
that heat much better than tiny babies can. Babies that small cannot regulate their temperature, and mom used to be the one providing that insulation and regulation.

Another analogy would be a neoprene wetsuit that you scuba dive with, or wear for water sports. Even though the wetsuit does not provide a water proof barrier, if you take that material and put a cross cut of it under a microscope, you’ll see tiny bubbles, these trap your body’s warmth and in turn keep you warmer in the water than if you had just a bathing suit on.
It’s wonderful to see he is a running, playing, full of life little boy!