3 kinds of materials that kill your wireless signal

Home wireless routers use radio frequency microwave to carry information. Microwaves are electromagnetic waves measured by wavelength or frequency. For example, the FM radio operate in the 88 - 108 MHz range, older microwave ovens operate in the 2.4 GHz range (yes, same as your CPU's frequency), wireless router 802.11a products operate in the 5 GHz range.

When you choose the location of your home router, you need to consider the radio frequency environment, which is strongly effected by the building materials in your house. Each structure or building material will provide a different degree of penetration to the radio signal. Depending on your purpose, sometimes you want to maximize the penetration, so that the signal can reach a bathroom on the other side of the house; sometimes you want to block the radio signal, so that war-driving hackers won't be able to catch leaking wireless signals on the street near home.

Structures that qualify as severe radio hazards are generally floor to ceiling structures that have a significant effect on the receive signal strength, either by completely blocking the signal or by reducing the signal strength by greater than 60%. Usually these structures are made of dense material and have varying degrees of metal associated with them.

1. metal is a very good radio blocking material -- as good as a mirror that reflects the magnetic waves (light to radio wave) at the surface, leaving no signal to penetrate through. Computer rooms are sometimes wrapped in a skin of metal shield which don't allow any signal to penetrate through. Your home constructions with metals are falling into this category, examples are mirrors, metal desks, metal room partitions, reenforced concrete floor, exterior walls, bathrooms, chicken wire mesh etc.
2. Dense materials like marble, bricks, water, paper allows radio signal to penetrate through while reflecting as well as absorbing some of the signal. Structures made of these materials can reduce the receive signal strength by 5 to 40%. You can find them by looking around: bookcases, filing cabinets, inner walls, kitchen table, fireplace, aquarium, bushes.
3. Materials that allow most of the radio signal to penetrate through are generally those materials which don't conduct electricity -- air, wood, plaster, synthetic material, asbestos and glass. Your celling, inner wall, window and door might be able to keep you warm and secure, but the signal from your wireless router pass through them as if they don't exist. This explains why when your pc looks for wireless in range, it finds all your neighbors' wireless routers a few inner walls away.