The triumph of the clear plastic bag

NEW YORK (CNNMoney) -- Recently I flew from New York to Hamburg, Germany, with a short layover in London's Heathrow airport. Since I was going only for a couple of days, I had no checked-in luggage; even so, British regulations require that anyone transferring flights has to go through security again, so I got in the long line with everyone else.

As I approached the X-ray machine, I saw a sign indicating that all liquid and gel toiletries had to be packed in a re-sealable, clear plastic bag no larger than 8 inches square. I briefly panicked. My toiletries were in a leather shaving kit; I'd not put anything in a plastic bag. Would security officials provide me with one? Would they confiscate my shampoo and toothpaste?

As it happened, no one said a word; my suitcase snuck through the X-ray machine without setting off any shampoo alarms. Which means that the plastic bag is unnecessary, right?

Well...not according to the regulations. And travelers appear to be following the rules. Ever since last August, when authorities in the U.K., U.S. and elsewhere began restricting passengers' ability to take liquids aboard planes, sales of plastic bags have seen a notable rise.

David Kellis, brand manager for the Glad bags division of The Clorox Company (Charts, Fortune 500), puts it this way: "It's rare that a new government regulation ends up requiring your product to be used."

The Heathrow restrictions that I avoided are typical. All liquids are limited to containers no larger than 100 ml (about 3.4 oz.). And they must go "in one transparent re-sealable transparent bag, no larger than 20cm x 20cm (8" x 8") in size, and fit comfortably inside the bag so it can be fastened closed." (Yes, that's right: doubly transparent.)

Moreover, Heathrow says, "the bag must be clear and re-sealable, such as 'ziplock' bags or bags with pressable seals. Larger bags or bags ... such as fold-over sandwich bags are not allowed."

This is not just a Brit thing. Since September 2006, the U.S. Transportation Security Administration (TSA) has required that passengers keep on-air liquid containers to a maximum of 3 ounces, and place them in a re-sealable quart-sized plastic bag. Presumably because so many Americans wear contact lenses, the TSA makes an exception for more than 3 ounces of saline solution and similar liquid or gel "items used to augment the body for medical or cosmetic reasons," but they must be declared separately outside the bag.

What has all this security meant for sales of the humble plastic bag? A marketing opportunity. Last winter, at least two plastic bag manufacturers handed out free bags in airports during peak holiday travel times, just to remind travelers of the virtues of their wares. Moreover, in February of this year, Hefty - a division of Pactiv (Charts) Corporation in Lake Forest, Ill. - began selling a flat-pack of 7 Hefty quart-sized OneZip bags, specifically labeled as meeting security guidelines.

Lisa Foss from Pactiv's media relations department declined to provide specific sales figures for the travel bags, but said that sales have been "strong and exceeding expectations." She added that sales of the company's normal quart-sized bags have also increased since last fall. Shares of Pactiv have risen about $4, to $32.40, since the U.S. restrictions were introduced last September.

David Kellis from Clorox said that prior to the new regulations, the quart-sized bag was not one of the brand's biggest sellers (consumers using bags at home appear to prefer the larger gallon-sized). Clorox's public filings lump plastic bag sales into a "specialty group" that also includes the company's wraps and containers businesses marketed in the U.S., charcoal, cat litter and food products. According to Clorox's most recent quarterly report, sales of the specialty group were up 7 percent, to $499 million, in the first three months of 2007 compared to the previous year. Clorox shares have also risen slightly since the September restrictions.

SC Johnson, which makes Ziploc brand bags, is a privately held company, and as such would not comment on sales.

Of course, if my experience is any guide, airport security officials may not always bother to enforce the plastic bag rule. After all, there has never been a publicly disclosed example of anyone using liquid explosives to do damage to a plane in flight, and many explosives experts downplay the significance of such a threat. Furthermore, anything you carry on board - liquid, gel or solid - goes through an X-ray machine, regardless of whether or not it's in a plastic bag.

But as long as the restrictions on liquids remain in place - and the TSA has indicated it has no imminent plans to relax them - the plastic bag manufacturers are more than happy to keep the supply coming.