Conductive polymer compositions

A conductive polymer composition, having positive temperature coefficient characteristics, comprising:

• at least one thermoplastic polymer having a matrix wherein a mixture of electrically conductive carbon blacks is dispersed,
• the polymer matrix constituting between about 20 and about 98 percent, by weight, of the composition and the mixture constituting between about 2 and about 80 percent, by weight, of the composition,
• wherein said mixture includes a first electrically conductive carbon black and a second electrically conductive carbon black, each of the carbon blacks having a structure level, as measured by DBP technique, of between about 40 and about 150 cc/100 g, and surface areas not greater than about 230 m.sup.2 /g, and each constituting between about 1 and about 40 percent, by weight, of the composition,
• the first carbon black comprising particles having an average size between about 35 and about 300 nm, and the second carbon black comprising particles having an average size between about 15 and about 25 nm.