To understand how different types of soundproofing foam can be used, one must first understand how sound waves and noise levels are measured. The ability of an object to block sound is measured by its Sound Transmission Coefficient (STC) rating, which can range from 0 to 100. A wall with a STC rating of 50, for example, means that noise levels on one side of the wall are 50 decibels higher than on the other side. Sound absorption is measured using the Noise Reduction Coefficient (NRC), which generally falls between 0 and 1. This number shows the amount of sound absorbed by an object, and the higher the NRC value, the more noise is absorbed.