Should the rough side or the fluffy side face against the airflow?

I bought an electrostatic furnace filter pad. It s just a sheet of material that need to be cut to the size of the air duct. I m not actually using it for a furance - I m sticking it into the air outlet of my dryer machine since it vents indoors and I m trying to reduce the amount of lint that spits out of the machine. This filter pad has a rough side and a soft/fluffy side. Does anyone know which side should be oriented against the airflow? That is, which side should be the "blowing" (not the suction)...?