When a rubber tree is tapped, a white liquid called latex bleeds from a fresh cut in the bark, the major constituent of which is a small carbon based molecule called isoprene. As the latex dries, the isoprene molecules begin to bind to one another and form long chains called polyisoprene. The long chains are intertwined and entangled, and they are quite happy to sit coiled up together due to an electrostatic attraction between them. When rubber is stretched, the individual polymer chains are stretched and line-up, and the order of the molecules is increased. This means that the entropy of the system is decreased and represents the force you feel in the rubber. When the rubber is released, all the chains pull back because this increases the entropy of the system. Explore natural rubber on the Institute of Making website: https://www.instituteofmaking.org.uk/materials-library/material/natural-rubber.