I looked everywhere online for a carpet chair mat that was 30” wide and could not find a single thing.  I was so confused — why are they all 36” but hard floor mats are 30”  FINALLY I found this one on Wayfair and it fits perfectly under my new L-shaped corner desk.  It’s exactly what I needed.  I also love that it ships flat so you don’t have to unroll it and wait for it to flatten in its own.  It is very sturdy plastic and lays wonderfully on the carpet.  Highly recommend.