Designed for the manufacture of electric parts, for use outdoors under: standard rel. humidity at (15-35)°C, 45-75% and at a voltage of more than 1000 V; at a temperature of (40±2)°C, (93±2)%, at a voltage up to 1000 V and a frequency of 50 Hz. They are characterized by high mechanical strength at moderate temperature, high stability of electrical properties at high humidity, high heat resistance