You can indicate which strategy you want to follow in the CMS.
Magento 1
Magento1 Admin Panel > System > Configuration > Catalog > Tweakwise > section Layered Navigation
The dropdown lets you choose between two options.
Query params = Magento's default strategy (so-called ‘ugly’ URLs)
URL segments = new Tweakwise strategy (so-called 'beautiful' URLs)
Magento 2
Magento2 Admin Panel > Stores > Configuration > Catalog > Tweakwise > section Layered Navigation
The dropdown lets you choose between two options.
Query params = Magento's default strategy (so-called ‘ugly’ URLs)
SEO Path slugs = new Tweakwise strategy (so-called 'beautiful' URLs)