NEW YORK (TheStreet) -- They make things like polymers, adhesives, resins, caustics, solvents, abrasives and ethers.They manufacture such substances as polyethylene and polyurethane and polypropylene and polybutylene terephthalate and ethylene dichloride and estrobond triacetin plasticizer, which is what becomes the filters on cigarettes. And they're as necessary to the civilization we find ourselves in as roads and running water. Chemicals: It's one of those behind-the-curtain industries no one thinks about (or wants to think about) until they drive by one of their sprawling plants, all smokestack and twisting pipe, like some science-fiction city -- or consider buying one of their stocks. It's an interesting moment for chemicals, split into two subsectors, the commodity chemicals and the "performance" or "specialty" chemicals. The chemical companies on our list of four -- Dow Chemical ( DOW), DuPont ( DD), Eastman Chemical ( EMN) and Celanese ( CE) -- are among the biggest and the baddest in the land, and they've all benefited since the second quarter from a potent combo: quickening demand, especially in export markets, and declining raw materials costs. This last dynamic is especially true in the commodity chemicals realm, where natural gas, a crucial feedstock, remains cheap.