What would be a stable way to hold lithium hydride powder?
If the LiH needs to be exposed to ambient conditions, it should be enclosed is a moisture-impermeable container, e.g., a glass ampoule which is closed off. Glass can be blown quite thin - but then you need to be quite careful. As DrMoishe suggested, PE or PP would be good, but I'm thinking of it as a closed tube, not as a binder.