These are the filters that are the cornerstone of the Chemex brewing process. They are thick. That's the point. These are for the 1-3 cup Chemex.
These bleached filters are the very cornerstone of the Chemex brew process: A Chemex without them is like a car without a steering wheel. Or like a yo-yo without a string. At risk of running our simile supply into the ground, suffice it to say that these are thick and sturdy, and help produce a clean and exquisite cup.