TT mats

@pbnaudio They’ve used Isodamp since inception. That mustard colored material is the Isodamp SD125 mat. Aero Technologies has discontinued the mustard color about a year, or so ago. New SME turntables will have black Isodamp instead. As can be seen on their website: https://sme.co.uk/audio/turntables/

Fremer actually mentions Isodamp in the very review you linked: https://www.stereophile.com/content/sme-model-2012-turntable-amp-312s-tonearm-page-3

Isodamp is great stuff, particularly when used as constrained layer damping. Because of it’s high price ($238 for a 4" X 4.5" X 1/8" square!), I chose to use the similar ASC Wall Damp for my constrained layer needs. A 4" X 4" square of Wall Damp costs only a buck or two. Of course, a turntable platter will look rather unsightly covered with 4" X 4" pieces, but ASC also sells it cut to size.

Hiraoka Diskmat SE22! Yes, it's vintage and I bought it brand new from Harvey Sound, NYC back in 1978! $20! Still in use on my Ariston RD11S! I have yet to see a better-made and sounding mat than this!

My experience is limited to a number of 401s with aluminum platters.
1. Boston Mat 2: energy suck, "cleaned" up the sound by removing microdetails including spatial cues, air and life.
2. Std. rubber mat: adds lushness and musicality. Smears mids and highs. Adds bass bloom.
3. 10" vinyl record: removes smearing and coloration (possibly due to the store and release of damping). Increase in detail, speed, air, transparency. Improved bass definition. Possibility of a little added brightness. This is what I use.
4. Cork, paper, felt, leather DIY mats: Meh. Not worth the effort.

@bdp24 Where are you getting Isodamp pricing? What you’ve posted is a nonsensical price.

Isodamp C-1002 Series 0.125" thick, 54" by linear foot is $68. That’s a lot of material. Can be ordered from the authorized distributor direct: https://www.rathbun.com/c-40-damping-isolation-materials.aspx

Michael Percy sells SD Series (what SME uses) 0.125" thick, 12" by 27" for $60. http://www.percyaudio.com/Catalog.pdf

Both sources have other thicknesses and sizes.