Carbon fiber manufacturer Zoltek Cos. announced on Tuesday a $300 million supply contract extension with its largest customer. The agreement with Denmark-based Vestas AS, the world's largest maker of wind turbine generators, is nearly triple the size of the previous deal between the companies.

A news release from the companies said Zoltek would provide $300 million worth of carbon fiber "over the first five years of the agreement," but did not provide other specifics.

Bridgeton-based Zoltek has supplied carbon fiber materials to Vestas for the past three years under a deal believed to be worth $80 million to $100 million, according to a report in March by Stuart Busch, analyst with RBC Capital Markets Corp.

Busch wrote in the report that carbon fiber is fast replacing fiberglass for turbine blades, because it makes the blades stronger and they also can be made larger.

The deal will help Vestas with its plans to open turbine manufacturing facilities in the United States, Spain and China. In a news release, Vestas suggested the deal also will help it bring wind turbines into wider use for creating energy.

Investors reacted favorably to the contract. In trading Tuesday on the Nasdaq stock market, Zoltek's stock rose $2.45, or almost 7 percent, to close at $38.09.