How-to completely BLACKOUT a room

[spm_uk]

Hey all,

im going to get a projector and i was wondering what is the cheapest solution to blackout windows? i was thinking maybe using FELT and some velcrow strips allowing easy apply???

any ideas

please link to material websites aswell cant really find any

Cheers

 

[spm_uk]

would the felt be thick enough to block the light you rekon??