Re: Which material is able to absorb, reject Bluetooth waves best?

Hello, Martin. Bluetooth uses radio waves at around 2.4 GHz, so we need to 
consider materials that will absorb / reject radio waves of that frequency.

According to this article, 
"There are all types of materials that may interfere with the propagation of 
the RF signal by absorbing energy. Typically, items with high water content or 
very dense objects will absorb radio waves. Examples of absorptive sources 
include paper, wood, dog food and kitty litter."

Absorption by water makes particular sense, because 2.4 GHz is the frequency 
used by microwave ovens and the energy is absorbed by water in the item to be 
heated.

However, you might want to consider some other alternatives for your effort - 
here is an Adobe Acrobat .pdf file that summarizes a study of various 
materials, including building materials, and how well they reflect and 
transmit radio waves at about 2.4 GHz:

Propagation Losses through Common Building Materials