Gutta-percha is a tree of the genus Palaquium in the family Sapotaceae. The name also refers to the rigid, naturally biologically inert, resilient, electrically nonconductive, thermoplastic latex derived from the tree, particularly from Palaquium gutta; it is a polymer of isoprene which forms a rubber-like elastomer.

The hardened milky juice of a tree, the Isonandra gutta, growing in Malacca and other parts of the Eastern Archipelago. It is much used as an insulator or constituent of insulators. Resistance after several minutes electrification per 1 centimeter cube at 54º C. (75º F.),  4.50E14 ohms. The specific resistance varies--from 2.5E13 to 5.0E14 ohms. A usual specification is 2.0E14 ohms. The influence of temperature on its resistance is given in Clark & Bright's empirical formula, R = R0 at, in which R is the resistance at temperature tº C--Ro the resistance at 0º C (32º F), a is the coefficient .8944. The resistance increases with the time of passage of the current, the variation being less the higher the temperature. Time of            Relative Resistance     Relative Resistance
Electrification.   at 0º C (32º F.)        at 24º C (75º F.)
   1 minute        100                     5.51
   2   "           127.9                   6.
   5   "           163.1                   6.66
  10   "           190.9                   6.94
  20   "           230.8                   7.38
  30   "           250.6                   7.44
  60   "           290.4                   7.6
  90   "           318.3                   7.66 In cable testing one minute is generally taken as the time of electrification. Pressure increases the resistance by the formula Rp=R (1+ .00327 P) in which Rp is the resistance at pressure p--R resistance at atmospheric pressure--p pressure in atmospheres. Thus in the ocean at a depth of 4,000 meters (2.4855 miles), the resistance is more than doubled. The longer the pressure is applied, the greater is the resistance. The specific inductive capacity of gutta percha is 4.2. Good gutta percha should not break when struck with a hammer, should recover its shape slowly, and it should support much more than 300 times its own weight.