They don't sell the thicker ones anymore:

https://olfa.com/products/olfa-rm-mg...ng%20workspace.

This link shows that the 3mm ones are discontinued:
https://olfa.com/collections/profess...en_cutting_mat

My local fabric shop has it advertised as 3mm but when I asked what the actual thickness of the mats in store was they realised they are now 1.5mm thick. She's changing their website.

Well like I said in my previous posts….my Olfa mats are OLD but they show on my ruler as closer to 1/16th than what you mentioned as 1/8”.

I recently purchased a Martelli mat. I cut out a bunch of squares and saw that they all weren't the same size. I thought it was me, a friend came over and used it, same thing happened to her. We got out a few rulers and measured the inch marks and some were off by 1/16 th of an inch. Then we used a yard stick and a measuring tape and discovered it wasn't 36" long either. I have called Martelli and am waiting for a call back.

good grief! They get a lot of mentions as good mats in this board. I hope it is a one off problem and they are good to deal with.

We probably never noticed because so few of us use the mats for measuring cuts. Sure fire way to wear out a mat.
I use my rulers and the fabric could be anywhere on the mat. The only markings I ever use is to refer to the measurements across the bottom if I want to be sure I have enough fabric.
When I go back upstairs I measure my mat measurements ;)

ok, measured my martelli mat with three different brand 6.5" rulers. The seems to lay perfectly at that measurement...but within the rulers the martelli 1/2" measurements seem to be just to the left of the cutting lines on the rulers.
Were I to use those lines I think my cuts would be about 1/16" off each cut, on the too big side.
But as I said I'd never use mat lines to cut with.

I'm new to quiilting, and I use cutting mats that are made for general crafting (not sewing specific). I haven't had problems with those. I've compared all of my quilting rulers (creative grids, omni grids) to my Alvins and they are spot on. However, it seems to me that for quilters, there might be a demand for a cutting mat with no markings at all.

I don’t often use my cutting mat lines to cut on but I definitely like and couldn’t do without the lines.
I line up folded fabric on them before I cut. Cut angles. Check selvages are square against them. Check blocks are square or triangles are triangular. Etc etc etc.