How can I make a custom attribute into a slider filter in Improved Layered Navigation?
It is required to create the new attribute with Catalog Input Type for Store Owner as "Price" from the beginning (this value cannot be changed after an attribute has been created).
With attribute created as a "Price" display mode "Slider" will be available under Improved Navigation tab.
Configure custom attribute units (inch, MB, px, etc.) and slider step size for the filter.