Many stretchy substances are made of long molecules called polymers. These might be natural polymers like latex or wool or man-made materials like polythene. In their relaxed state these long molecules tend to ball up to some extent. So when we stretch the material, we are straightening out the molecules.
Rubber is an example of stretchy substance. It can be found naturally or can be made in the laboratory. Rubber contains polymer polyisoprene (−CH2−C(CH3)=CH−CH2−)n that is composed of thousands of isoprene monomers CH2=C(CH3)−CH=CH2. Polyisoprene strands stick together by forming electrostatic bonds, much like the attraction between opposite poles of two bar magnets. The attraction between these strands holds the rubber fibers together and allows them to stretch and to recover.
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