Which materials inhibit of cell-phone signal transmission?
Today's new home and building constructions are being built with new and innovative energy-efficient technologies like roof membranes and extra insulation. Many of these buildings are being constructed on very tight building envelopes. A typical new house constructed today with plaster, drywall, wood, and glass, could typically lose up to 30 dB or more of cell signal.
Metals like brass, aluminium, steel, copper, iron, and so on are the number one culprit for blocking cellular signal. The next problem arises with another energy efficient material, and that is low-E glass (Low Emissivity Glass). It is wonderful for keeping heat out but it also reflects cellular signal back. Concrete, cement, bricks, plaster, plywood, solid wood, clear glass, fibreglass insulation, and drywall are all great at dampening down cellular signal.
Basically, the building materials that provide the most structural strength and the best insulation can be the worst offenders when it comes to reducing indoor cell phone signal coverage. Read a blog post which explains this topic about things that block cell signal in more detail.