Chewing gum has been with us since the Stone Age – chicle gum was made from the sap of the Sapodilla tree. Most modern gums are based on a synthetic equivalent, a rubbery material called polyisobutylene that’s also used in the manufacture of inner tubes. Polyisobutylene is mixed with plasticisers and materials – all food grade – to make the gum mixture chewable. The success of chicle and polyisobutylene lies partly in the narrow temperature range over which materials soften. So a material that’s firm and easy to mould becomes soft and pliable in the warmth of the mouth. Via What’s chewing gum made of?