What is the story with schach mats?

Years ago, “putting up schach” referred to the tedious process of placing hundreds of single stalks of bamboo or lath across the top of one’s sukkah. Today, this task has been greatly simplified due to the proliferation of schach mats. However, mats that are made for sitting are not kosher for schach⁸. Because these mats are made in a part of the world where it is common to make mats for sitting, it is imperative that one’s schach mat comes with a reliable hashgacha.
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8. Shulchan Aruch (O.C. 629:6)