Is this is double-sided plane? I have a hair object, and I wonder how it was done.



Is this hair composed by planes? 
And if yes, are they double-sided? To me it looks double-sided because it is also visible from the other side.

I have also uploaded the project here if somebody needs to take a closer look.

Thank you very much!
No they are not double sided. You can check this by going to the N menu and checking Backface Culling under Shading options.