The discovery of letters containing anthrax in the United States in October generated nationwide fears about the safety of the U.S. mail system. American envelope makers have been rushing new products to market in an attempt to calm consumers.

One company, Mail-Well, is experimenting with the idea of making envelopes out of a material that will turn brown if it touches certain bacteria, such as anthrax. The firm is also stepping up production of an old design, which has a window on the bottom of the envelope.

"We say with this window on the bottom - we call it a 'visulope' - if something is in there, then you would see it in the envelope," said company president Bob Hart. "How do you insure a higher degree of confidence? These are some of the things that we, other envelope makers, and our suppliers are working on."

Mr. Hart says the industry is over-reacting to a relatively minor scare. He points to the numbers as proof. "If you think about the number of envelopes mailed [in the United States, it's] 210 billion a year. We make 45 billion of that. And just four envelopes had anthrax in them," he pointed out.

Why, then, are all the envelope manufacturers going to the trouble of creating new, anthrax-safe products?

Because, says Lester Stern of the National Envelope Corporation, when it comes to sales, consumer perception is more important than reality.

"If your consumer has a concern and it is a legitimate concern, whatever business you are in, you react to it, not necessarily because you think what you are doing is not safe, but because you have enough people out there saying we want something else, and so you react. Any good businessperson does that," he said.

Mr. Stern's company is manufacturing transparent envelopes so nothing can be hidden inside, envelopes with extra gumming on the side seams, and envelopes with special security flaps - all in response to consumer demand.

"You are always listening to them very carefully for trends and for desires that they have if you want to continue to be profitable and grow your business. I think the way we responded to this anthrax is part of an entrepreneurial desire to always be flexible," he said.

Since there are about 200 envelope manufacturers in the United States, Mr. Stern says the public can expect many new envelope designs this year.