Aluminum can block NFC (Near Field Communication) signals to some extent. NFC operates at high frequencies (13.56 MHz), and materials such as metals, including aluminum, can interfere with or block these signals due to their conductive properties. When an NFC-enabled device, such as a smartphone or a contactless card, attempts to communicate with another NFC device, the signal may be attenuated or completely blocked if there is a significant amount of metal between them.

However, the extent to which aluminum blocks NFC signals can vary depending on factors such as the thickness of the aluminum, its proximity to the NFC devices, and the specific NFC technology being used. In some cases, thin aluminum may allow NFC signals to pass through with minimal attenuation, while thicker or denser aluminum may block the signals more effectively.

In practical terms, if you're trying to use an NFC-enabled device near aluminum, the effectiveness of the blocking can vary. In general, it's best to minimize the amount of metal between NFC devices to ensure reliable communication.