While foil can block radio waves, it's not effective at blocking GPS signals. GPS devices use a different type of radio wave than cell phones and Wi-Fi, and the wavelengths are longer. Foil simply isn't thick enough to effectively block those signals.

Here's why:

* GPS signals are much longer wavelengths: GPS signals are in the L-band, which is a much lower frequency than the radio waves used by cell phones and Wi-Fi. This means they have longer wavelengths and can penetrate materials more easily.

* Foil isn't a perfect barrier: While foil can reflect some radio waves, it's not a perfect barrier. Some signals will still be able to pass through, especially if the foil isn't completely sealed.

* GPS devices are designed to be resistant to interference: GPS devices are designed to work even in challenging environments, such as cities with lots of radio interference. They have multiple antennas and use complex algorithms to filter out noise and receive a strong signal.

In short, using shiny foil to block GPS signals won't work. You'll need a much more sophisticated method, like using a Faraday cage, to effectively block GPS signals.