A reader noticed this label on a carpet:

More specifically, this:

My first thought was, how do they know? What if I can identify one of the fibers? Can I sue because I was promised a mystery rug?

It turns out that products covered by the federal Textile Act have to be labeled to show the fiber content. You can see how that would be helpful to someone who specifically wants cotton or wool or whatever. But the regs require the label even if nobody has a clue what's in the product:

If a textile product is made—in whole or in part—from scraps, clippings, rags, secondhand fibers or fabrics, or other textile waste materials of unknown and, for practical purposes, undeterminable fiber content, the disclosure may indicate that this is the case. [One example: "Secondhand materials—fiber content unknown."] If on the other hand, the fiber content is known or can be readily determined, the full content disclosure must be given.

So basically this statement on a label means "we don't know what's in this and frankly, it'd be hard to figure that out even if we tried." I guess they didn't put an exclamation point on the end ("Made from 100% Unidentified Fiber!), but it still sounds a little like a sales pitch based on not knowing what they put in the thing.

Their real problem might be the "Made in America" claim, though. They can't say that unless "the product is made completely in the U.S. of materials that were made in the U.S." (Emphasis added.) So I guess my question is still, how do they know?