You can indicate which strategy you want to follow in the CMS.

Magento1

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)

Magento2

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)