The quick answer

Open the Loot Filter with Shift + F by default. Rules are evaluated from top to bottom; the first matching rule wins. Put a rule that keeps a valuable Unique helmet above a rule that hides helmets generally.

Create or import a filter

  1. Create a filter in the interface. Put rare items you need, target bases and useful affixes above lower-value hide rules. A looser campaign filter is a practical starting choice; tighten it as your needs become clearer.
  2. Import a compatible filter through the clipboard option or the filter folder opened by the interface. Select the imported filter and check the creator’s version and strictness before relying on it.
  3. Compare the behavior with a known item. Hold X (the default key) to temporarily disable filtering and show all drops. If an important item appears only then, inspect which hide rule matched it first.
  4. Revisit the filter when changing bases, damage type or mastery. An endgame filter is not automatically suitable for a new character.

Limits and verification

The official 1.4 change increased the rule limit to 200. An older guide value of 75 should not be used as the current limit.

Test imported filters with your own items before relying on them.