Most bottled ready-to-drink coffees are packaged in plastic bottles, often specified as PET (polyethylene terephthalate).
Instant coffees are mixed with hot water or milk and are ready in seconds (often advertised as 'instant' or ~30 seconds). Bottled cold-brew and other ready-to-drink coffees are pre-brewed and ready to pour and serve from the bottle.
Instant mixes advertise readiness 'in an instant' or in about 30 seconds when mixed with water. Bottled ready-to-drink coffees are pre-brewed and ready to pour and serve immediately.