Wonder Woman Cape Adult - 21237, Size: Standard

Q: how does it attach? to stay up, velcro around the neck or what?

It fastens with Velcro in the front.

Q: Is this cape dual sided. Can it be used on the blue side?

Yes! It's reversible. But the WW insignia is on the Red side. Quality of this costume cape is Excellent.

Q: What is the fabric made of? satin? i'm trying to match it to d.c. comics wonder woman satin boustier.

The Red Lining and Stars are Satin not first class type but classy enough, the gold is not it can fade within 3-4 times of washing ... mine lasted longer 10 timesup to now it still looks new because I handwash with body wash soap not laundry detergent .... to keep the integrity of the cape... hope this helps... it is a good buy