No, it is made of breathable polyester designed for moisture-wicking and thermal insulation inside a bag. It is not intended for use as a standalone waterproof shell.
Yes, the flexible polyester cloth allows it to conform to both rectangular and mummy-style sleeping bags without bunching.
This inner warmed liner typically adds between 3°C to 5°C (5°F to 9°F) of extra warmth to your existing sleep system.