Absorption of digital hash

Berkeley uses material to absorb stray digital noise. Anyone know what they use?

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I use Mu Metal foil to shield my step up transformer from external EM fields and resulting noise. Works great.  The difference in noise levels is clearly audible. 

I used my golden plate homemade device : a plate of shungite with an external copper tape face + in some case mineral as quartz to fine tune the sound...😊

I used mostly  very thin plate unlike the example of this image


Thanks guys. I've found Holland Sheilding System as a result of your helpful comments. Now will do some shopping :)