......and thank you for understanding what we aspire to. There is a truly high degree of satisfaction involved in achieving excellent results at the lowest cost possible, and using materials that would otherwise not be considered as being used.
Black Out Cloth is exactly that...and simply serves the other purpose because one side is white (coated side), relatively smooth, and it's somewhat inexpensive. It can also be had in "out-sized" proportions. However it remains a "low performance" option in the raw compared to being painted upon...and the construction of a suitably rigid frame can be a daunting task to some.
Spandex is MUCH more easy to work with...cost about the same as Black Out Cloth...and is much lighter in weight. A Frame need not be made nearly as sturdy since the degree of stretch pressure is much less. Spandex mostly finds favor amongst those who want a Acoustically Transparent Screen to place speakers behind, and want it to come at a extremely reasonable budget. Say...5x less expensive.
Now some have taken Spandex to breast because it is simply an easier Build than Black Out Cloth, and in the Silver metallic form, offers performance BOC cannot.
Myself...I prefer painted surfaces because they can be ANYTHING
I wish them to be, and ideally configured to ANY
PJ & viewing circumstances. That's important to me...and many others because compromise does not have to go hand in hand with "less expensive", and when you can achieve high performance levels at an extremely lower cost, your satisfaction index soars...and it all seems to have been all the more worthwhile an endeavor.