The Lian Li TU150 doesn’t come with any dust filter at the bottom. As the bottom fan is responsible for the intake of air, it will be dusty.

Benjamin recommended me to get the DEMCiflex Dust Filter ST30 Double 120mm from Amazon.

DEMCiflex Dust Filter ST30 Double 120mm - Packaging Front
DEMCiflex Dust Filter ST30 Double 120mm – Packaging Front