A loophole in San Francisco's pioneering plastic bag ban has now led to existential questions about the nature of the reusable shopping bag.

The city is upset because it thinks a bunch of grocery stores were thumbing their noses at the spirit of the ban. As it stood, the only kind of bags that stores could use were paper, or reusable bags, which had to be made of cloth, fabric or 2.25 millimeter-thick plastic.

"They're giving out bags that are 2.25 mil thick," said Jack Macy, of San Francisco's Department of the Environment. "But they're not very durable, they rip, tear, break and stretch out easily."

So the city decided to change the definition of a durable plastic bag to one that can be put in a washing machine with hot water, used 100 times and carry 20 pounds.

This makes the bag men unhappy. Rioplast Industries' Chairman Robert Berman came to the public hearing on the new definition Tuesday afternoon, afraid that his thick plastic bags won't be used by stores anymore. Berman took exception to the notion that a bag should withstand the slings and arrows of a washing machine to be considered "reusable." He said people just wipe off his plastic bags with a sponge.

"The implication to us is that this is targeted to include only cloth bags," said Berman. "It seems to be designed very specifically to exclude our product, and we don't understand why."

The redefinition was adopted at the end of an hour-long discussion, which featured several theories about why a plastic bag ought or ought not to be put through the spin cycle to prove its reusability.