Almost every bad chair-mat purchase is the same mistake: buying a mat for the room instead of for the floor. The two families are not interchangeable and they are not marked clearly in listings. A carpet mat has cleats or spikes moulded into the underside - Gorilla Grip describes hundreds of spikes on its carpet mat, and Floortex calls the equivalent a gripper back - and those cleats are what stop the mat wandering as you push off. Put that same mat on hardwood or LVP and the cleats bear directly on the finish. Gorilla Grip's own instructions for its carpet mat say not to use it on hard floors. A hard-floor mat is the inverse: smooth or rubber-backed underneath, with nothing to bite into pile, so on carpet it slides out from under the chair on the first hard push.
The second thing listings hide is pile height, and it is the number that decides whether a carpet mat works at all. Floortex rates the Valuemat for carpet piles up to 1/4 inch including the pad. HON says its mat works best with 1/4 inch pile. The Staples mat is rated for flat commercial pile up to 1/8 inch including padding - which is thinner than most residential carpet, and is the reason a perfectly good mat can feel wrong in a spare bedroom. Measure the pile with a ruler pushed to the backing before you buy anything; if it is over a quarter inch, plastic will sink and divot no matter what the box says, and tempered glass is the honest answer.
Material is the third axis, and it is really a lifespan question. Floortex's own materials guide puts vinyl at the light-and-occasional end, polycarbonate at the heavy-use end, and tempered glass above both, describing glass as something that will never sink, curl or bend. That maps to what people report after a few years: thin PVC mats crack and cloud, and the repeat recommendation in r/BuyItForLife and r/homeoffice threads about mats that failed is tempered glass. Lorell rates its 1/4 inch glass mat to 1,000 lb and backs it with a 5-year limited warranty, versus the 2-year limited warranty Floortex puts on its vinyl mat. The trade is money up front and weight - a glass mat is a two-person carry and cold underfoot.
Size is where people under-buy. Floortex's sizing guidance is to measure the furthest points the chair actually travels, including sideways to reach a drawer, and then add the lipped section that tucks under the desk. A lip is not decoration: it is the part that stops the front casters dropping off the edge every time you tuck in. A 36 by 48 inch rectangle with no lip is the smallest thing that works for a single-monitor desk, and it is genuinely tight.
We research these from manufacturer specifications and published documentation. We do not run wear testing, so where a thickness, load rating or pile limit is the manufacturer's claim, this page says so.