Kong Company Extreme Kong. This super durable almost chewproof Extreme Kong is the ultimate in a dogs chew toy. Kong Extreme can be stuffed with treats too. This Kong Extreme cleans teeth and conditions gums. This Kong Extreme Kong is made of the exclusive Ultra-Flex carbon black formula – world’s strongest dog toy rubber. Recommended for dogs that are tenacious chewers. Kong is being used worldwide by police K-9, drug enforcement, and military K-9 teams. This dog toy can withstand hours of chewing. Made in USA dog toy.