Does PLA block wifi signals? I printed a raspberry pi case from PLA. This case.

I fitted it to my raspberry pi and now the wifi keeps dropping out. When I take it out of the case there is no problem. 

The filament I am using is Black, 3D Hero 1.75mm.

Has anyone experienced anything like this before, if so how did you work around it?
Is it common with PLA is there another material that wouldn't cause an issue?
Typically the black pigments in polymers are mineral based. If you are having true WiFi issues then it sounds like your filiment is using black iron oxide also called magnetite for the black pigment. This is the same material they use in radar absorbing paints which would make sense as to why you are having radio related issues.