Pressurized portafilters are standard in many entry-level and mid-range espresso machines. They're designed to help beginners produce decent-looking espresso even with less-than-perfect grind size or tamping technique.
These portafilters feature a double-wall basket with a small hole or valve that restricts water flow. This design artificially creates pressure regardless of how the coffee is ground or tamped, resulting in a consistent crema on top of your espresso.
Pressurized portafilters are an excellent starting point for espresso beginners, allowing them to produce acceptable results while learning the fundamentals of espresso preparation.