Exotic
But I'm wondering how far away this is from the "gel" propellants Rocketdyne have pushed for *decades* apparently with *no* success?
That said the launch was impressive and being a monopropellant makes it more challenging.
*if* this uses a catalyst this might be a way to get the stability of solids with some of the performance of liquids in a safe package.
That's a *big* if.