As I mention each and every week, Marketplace is a 22 minute show and they did a 10-product countdown, giving them approximately 2 minutes per product, so they had to leave a lot of information out.
So, what does J-Cloth claim? Apart from being a re-usable, machine-washable, lint-free paper towel replacement, which they've established a long time ago, J-Cloth claims that its biodegradable offering is fully biodegradable, because it's made from biodegradable fibers. When called by Marketplace, they said that the fibers were cellulose from wood pulp. Unfortunately, their website doesn't seem to have any further details that I could find—and cellulose can mean a lot of things, from cotton to rayon to paper, all of which are biodegradable.
Marketplace says the biodegradable seal on the package is invented and doesn't represent any certification mark, and is there to "look official". When they asked the company, the company said that J-Cloths could go in a municipal green bin for compostable waste. The critic says J-Cloths are not certified compostable and so the city compost teams will pull it out and divert it to the landfill, and landfills are designed air tight and water tight and basically, nothing ever composts in them.