Roulettes are meant to stay at a roulette table; they never go to the cashier's cage to be cashed in. They are changed for cash chips before a person leaves the roulette table.
This means they don't need as many security features and are generally made cheaply - no spots, no inlays, etc.
Physically, they can be the exact same materials and manufacture as other chips, but casinos may use a different type of chip for roulette than cash... It varies.