There are a few important settings regarding SEO. Find them in this section:

Magento1 Admin Panel > CMS > System > Configuration > Tweakwise > section Layered Navigation

This article explains these settings further.

Max allowed facets for indexing

Attributes which will have a noindex/nofollow

Add canonical tag to category page

Query parameters not considered in navigation URLs

Ignore params in the URLs.

Filter combinations allowed for indexing

 

Filter combinations that you DO want to index. This works as follows:

By default, a page will not be indexed if you filter just once. This option allows you to indicate for which filter value you do want indexation.

There are three settings that determine if a filter is display as non-indexable:

• filter combination whitelist
• filter blacklist
• max facets

If a filter is on the blacklist (so it's non-indexable), but there is another filter that causes the combination to be in the Filter combinations allowed for indexing, then the filter URL will be rendered indexable.

The combinations are checked first, so when that combination is deemed valid, then this will have priority over other settings.