Turntable Mats: Rubber, Felt or Cork.

@uberwaltz
I posted this on my Virtual System
"Added a black aluminum 20mm oversized platter to the slate plinth 401. Beautifully made. I did some listening tests before and after swapping out on a number of tracks (after all the tubes were warmed up for an hour.) Definite increase in bass control. I’ve been having some issues with a little bloom in the low end which have been tamed. Color, speed and focus -especially in the mid bass- is improved by a considerable margin. The sound stage narrowed a little for the first few tracks but seemed to be result of improved focus and increased stability of image placement. An upgrade, at around $750 inc s/h that puts a smile on the face.".

NOTE - the soundstage narrowing comment above is moot. The effect disappeared the next day while focus remained fine.

@poko See my post on 10" vinyl mats.

@lewm
I agree with your comments and others should also be aware of the default subjectivity of my notes.
Some additional notes. First off, I have an almost eidetic and long memory when it comes to the senses. I can’t help it. I also prefer a brighter, transparent and airy sound. Second, my grading of the mats is obviously based on my system and how I hear the mats. I noted in my post that it was non-scientific. I also used the 10 point scaling to denote the differences with more granularity.
Third. I stand by my comments on the BM2. Damped the hell out of the music. Lastly, while I did comment on Slaw’s MyMat, and suggested it sounds pretty good, it is not my intention to promote it. That’s why I made the disclaimer in an earlier post that Slaw sent me a mat to try. It simply is one of the few mats I had to make some comparisons. Certainly, the OP should try other mats. Nowhere did I suggest that more expensive mats like the gunmetal suggested by Chakster would be inferior or not options. Thanks.

@pryso Precision Audio Components 
https://www.classichifi-shop.co.uk/product/aluminium-platter-20mm-over-sized-satin-black-finish/

Just to clarify, I use the bare platter most of the time. Sometimes a recording is just too much. That’s when I throw on the MyMat to take the edge off without losing the essence. Being thin, there’s no need to adjust VTA.
Disclaimer: Steve sent me an early version to try.

I also tried Slaws MyMat. Some non-scientific notes below from memory. VTA was adjusted for thickness.
Musicality/Detail/Soundstage/Quietness
Boston Mat - 5/5/6/10
Rubber - 7/6/7/7
Cork - 6/6/7/8
Vinyl 10" EP - 9/9/9/6
Bare PAC aluminum platter 10/10/10/7
MyMat 9/8/7/8

I tried a Boston Mat2 on my 401 years ago and sent it back. I have comments in another thread. Basically, while it did quiet things down by removing background grunge and offered what I'd call a stable panorama, it also removed the life and soul of the music to the point of my disbelief.