After Karel Appel, Constant and Corneille had found each other in Amsterdam, they founded on December 16, 1947 Reflex, Dutch Experimental Group. The three blood brothers dipped their hands in paint and formed an alliance by printing these hands on a large sheet of paper: a rare moment of unity between very different characters.

This was followed by a second establishment in 1948 with more artists and poets. These included Constant Nieuwenhuijs, Asger Jorn, Karel Appel, Guillaume Corneille, Eugène Brands, Anton Rooskens, Theo Wolvecamp and Jan Nieuwenhuijs, also a member of the CoBrA movement, and later all the poets Gerrit Kouwenaar, Jan Elburg, Bert Schierbeek and Lucebert. As an example of the group served the Danish artists group Høst.

The group experimented with new colors, shapes, materials and subjects. The group also gave a magazine, called Reflex. This was also called the body of the group. The name Reflex was therefore also sometimes used as a name for the movement. The first issue of the magazine appeared in September 1948 and contained the manifesto of the CoBrA movement of the painter Constant. The second and last issue appeared in February 1949.