Sealed System

A vacuum whose airflow path is engineered so that every cubic foot of air passes through the filter before exhausting. Joints, hoses, and seals are designed to prevent bypass.

Without a sealed system, a HEPA filter is largely irrelevant. Air takes the path of least resistance; if there's a leak in the body, air bypasses the filter. Miele, Sebo, Riccar, and a few others ship sealed systems by design.