Ok so, I saw this video:Hackweek 2015 - YouTube
and I wanted to try to make it myself since he kinda showed how to do it in parts of the video but when i did it would just detach and do this:
I wouldn’t really recommend this, many things could go wrong:
Physics messes up and causes object to go flying to orbit at maximum speed to the null zone.
Increase lag and physics activity leading to performance problems.
Parts spazzing everywhere causing an unsatisfying cloth physic.
Collisions (Unless you turn them off :P)
And much more, if you really need something that reacts like a cloth however, using a beam thats attached to one anchored brick thats attached using a rope constraint to another brick thats anchored can provide more reliability however, it wont give you the bending and folding action as a cloth would have.
Probably can get something that might look similar, a lot of flags are made out of beams nowadays. But from the video it seems this is reactive to physics.