Bellows refer to an "elastic", accordion-like, connection between coaches, made usually of rubber or leather, to protect the transition between two coaches from weather and drafts.

These are used for the first time in Europe at the end of the 19th century, but from the middle of the 20th century they are increasingly replaced by rubber bead transitions which are simpler and do not require additional operations to connect or disconnect during coupling / uncoupling of two coaches.

Bellows are still largely used:
- in the case of narrow-gauge railways with tight curves: the rubber bead does not follow curves as flexibly as bellows;
- for permanent and semi-permanent coupled multiple units: as there is no need for constant coupling / uncoupling operations, bellows are used due to their better sealing capacity.

The rubber bead transition consists of two vertical and one horizontal bead, made of an abrasion-resistant rubber compound, which are attached to the car body with clamping rails on both sides and above the front door.

Rubber bead transitions are standardised in UIC Code 561 - transfer devices for passenger coaches. The clear width of the transition is 1060 mm, the middle of the upper bead is installed 2255 mm above the buffer level, the center-to-center distance of the side beads is 1360 mm. The rubber bead is equipped with a foldable transition bridge that is at least 940 mm wide. Rubber beads can be equipped with connecting elements for mixed coupling with bellows transitions.

In contrast to bellows, no additional operations are required when coupling or uncoupling two coaches. That is why the rubber bead has almost completely replaced bellows in single wagons of mainline railways, with two main exceptions:
- the case of narrow-gauge railways with tight curves: the rubber bead does not follow curves as flexibly as bellows;
- permanent and semi-permanent coupled multiple units: as there is no need for constant coupling / uncoupling operations, bellows are used due to their better sealing capacity.