Multilayer adsorption occurs when the initial layer of adsorbed molecules provides a new surface for additional layers to adsorb. This is often described by the BET theory (Brunauer, Emmett, and Teller), which extends the Langmuir model to account for multilayer adsorption. According to BET theory, the adsorption process does not stop at the first monolayer but continues to form multiple layers, especially at higher pressures.
