Magento Open Source, 1.9.x

Filterable Attributes

Each attribute that appears in layered navigation is set to “Use in Layered Navigation.” The filterable attribute can be configured to display the results, which is 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.

Setting up anchored layered navigation is a two-step process. First, you need to set up the filterable attributes. Then, make sure the category where the attribute is used is an anchor category.