The o-ring cord is a rubber cord, obtainable in many sizes. The o-ring cord can be vulcanized to form an o-ring and is often used when you need a special dimension, since you can customize the seal to the subject, and at the same time this solution is relatively in-expensive.
Seals made of o-ring cord is only recommended for static solutions.
The rubber material depends on the area of application, for instance: NBR, FKM, EPDM, silicone etc.