Helium-filled balloons often have plastic ribbons and other items attached such as plastic valves, tie-off discs, and clips. These attachments are used to seal the air or helium into the balloon as well as attach ribbons and groups of balloons together. These attachments are usually made of plastic and also become litter when released with balloons.
Standard plastic attachments include plastic clips, discs, cups and valves (seen below).
It is not unusual to find plastic ribbons attached to balloons as well as ribbons that have become unattached. Cotton string may be biodegradeable but it is still an entanglement and ingestion threat to wildlife and not considered an acceptable alternative.
Balloons may also be found with other attachments, many made with plastic, all becoming litter once released with the balloons.