Is it better to have models that have double faces or is it better to have a two-sided material instead? - Pipeline & Plugins - Epic Developer Community Forums
Daily Blender Tip 350: Double-sided materials - BlenderNation
Double-Sided Materials in Blender - YouTube
how to create double sided materials in blender - YouTube
Blender Tip - How to make Double Sided Materials - 217 - YouTube
How to add Blender 2 sided material to one mesh - cgian.com