A transport ticket is often loaded onto a reusable contactless support. The important distinction is between the object in your hand and the fare product stored inside it, then between tickets that are personal and tickets that can be shared.
Two cities, two local wallets
Madrid lets one card carry companions
The Multi card can contain up to three non-personal fare products. Several travellers can use the same card at the same time when they share the route, validating once for each person.
Barcelona separates support from ticket
The anonymous cardboard T-mobilitat support is contactless, reusable and sold at metro machines. It can hold non-personal products such as T-casual, T-grup and T-familiar, while personal products follow different rules.
A tourist pass is another Barcelona choice
Hola Barcelona travel cards provide unlimited travel for a selected 24- to 120-hour period from first validation and include the metro journey to and from the airport. Compare that clock with the number of rides actually planned.
Sharing belongs to the ticket, not the plastic
A reusable card does not automatically make every fare shareable. Read whether the loaded product is personal, multi-person or valid for simultaneous companions before passing it back at the gate.
Start fresh when the city changes
Keep useful cards for a return visit, but do not expect a Madrid validator to read a Barcelona travel product. Check the local transport authority at each destination and buy for that city's zones, airport rules and trip pattern.