All landscape fabrics stop some weeds from coming through from below, but certain aggressive weeds will penetrate any landscape fabric especially if there is a heavy load of mulch on top.
These weeds that are in the ground are only the initial problems. Long-term, 95%+ of weeds come from germinating seeds in the top mulch. Ideal (low) permeability landscape materials like 5-Year, 10-Year, and 20-Year Weed-Shield, Weed-X, and Weed-Proof PLUS, prevent most weeds from reaching the ground, with 20-Year Weed-Shield and Weed-X being the most effective. Higher permeability landscape fabric, however, has larger and more holes that not only allow more water through but also allow roots through.
These roots establish themselves below the fabric where they thrive and are difficult to remove.