Magento Open Source, 1.9.x
Filterable Attributes

Layered navigation can be used to search for products by category or by attribute. For example, when a shopper chooses the Apparel/Shoes category from the top navigation, the initial results include all products in the shoes category. The list can be filtered further by choosing a specific color or size, or by specifying values for both color and size. For an attribute to be included in layered navigation, its property settings must be set to make it filterable.

Anchor categories can be set to appear in an additional section that filters the list by attribute value. The attribute section appears only if a category is set to “Is Anchor.” Each attribute can be configured to display the number of matching records found.

The attribute properties, combined with the product properties, determine which attributes can be used as filters for layered navigation. Only those with the catalog input type of Dropdown, Multiple Select or Price can be used as filterable attributes.

Filterable Attributes In Layered Navigation