Hide the case and air parts (if they are showing).

Select the filter.

Open the Materials quick edit dialog in ONE of the following ways:


Material DB Name = My Materials
Type = Resistance
Name = Baffle

Flow Direction: Click the ... button
Click the Z button on the Flow Direction dialog.

(On the Material quick edit dialog) Normal Direction 1 = Global X.
Normal Direction 2 = Global Y (automatically selected).
Click Apply.