These felt mutes have been specifically designed by a trumpet player after experimenting with various types of mutes and thicknesses of felt. After trial and error and live tests in London Venues a blend of felt fabric was chosen. 
The mute comprises of 2 layers, 1 Layer is slightly thicker than the other and is a great balance.
The effect is a reduced volume and reduced high frequencies whilst not restricting air flow too much. 
This creates a Flugelhorn type effect which can be further exaggerated with a deeper mouthpiece cup should you wish. 

I have a few other colours which you can see in the photos....so please check you're buying the colour you want. 
They are all reversible with white being the 2nd colour.

A London venue with sound limitations inspired this journey of discovery and this video is an example of what sound can be achieved with felt mutes - https://www.youtube.com/watch?v=Zo0Zn1Xl0ms

Enjoy!