Hi Even, this is quite a common problem. There are a couple of things to consider when deciding if Noindex is the solution rather than robots.txt.
Unless there is a reason the pages need to be crawled (like there are pages on the site that are only linked to from those pages) I would use robots.txt. Noindex doesn't stop search engines crawling those pages, only from putting them in the index. So in theory, search engines could spend all there time crawling pages that you don't want to be in the index.
Here's what I'd do:
Decide on a reasonable number of facets, for example, if you're selling TVs people might search for:
- Sony TV (Brand search)
- 50 inch sony tv (size + brand)
- Sony 50 inch HD TV (brand + size + specification)
But past 3 facets tends to get very little search volume (do keyword research for your own market)
In this case I'd create a rule that appends something to the URL after 3 facets hat would make it easy to block in robots.txt. For example I might make my structure:
- example.com/tv/sony
- example.com/tv/sony/50
- example.com/tv/sony/50/HD
But as soon as I add a 4th facet, for example 'colour'- I add in the filter subfolder
I can then easily block all these pages in robots.txt using:
Disallow: /filter/
I hope this helps.