We built a surprising feather-light weight shield this past event that held up extremely well to blows, although I would caution against falling on it with your full body weight. IT was made using house insulation, strapping tape with the fiberglass strands through it, duck tape and soft foam. If you were curious, i'd be willing to share. It's not for everyone, but alleviated the weight associated with a shield. Weight doesn't matter as much as you are not supposed to be rushing or shield bashing anyways.
Realms of AdventureLive The Magic!