urethane rubber for mold making

Has anyone use urethane rubber/plastic for mold making for fiberglass/carbon lay up? what’s the pro and con versus fiberglass mold?

I’ve attempted to vacuum form a 2mm thermoplastic that is self releasing. In theory it would be good for making small moulds. But you’d have to keep an eye on the heat when curing.
Its ironic I’ve not had the time to refine the process due to making fibreglass moulds:rolleyes: