It doesn't really matter what the black material used to wrap the windows or facades of buildings with, is made of. It can be cloth, garbage bags, plastic - as long as it's black.
Every individual artist, cultural sector employee, or concerned citizen is invited to participate. You can get the "Tegen de sloop van de kunst" (Against the demolition of art) posters by sending an e-mail to halbe.de.sloper@gmail.com.