Natural rubber which is a polymer of 2-methyl-1, 3-butadiene, their polymeric chains are held together by weak Vander Waals interactions. So it becomes soft at a temperature above 335K and becomes brittle at low temperature below 283K. The natural rubber also tends to get attacked by oxidizing agents. To improve these physical properties, cross-linking is done which helps to bind it's planar polymer sheets thus increasing elastomeric properties, thermal stability.