Abstract: A portable, reusable concrete form is set forth. At least two substantially identical wall sections have inner walls cooperating with one another to form an elongate cavity of desired transverse cross-sectional shape, being that of the concrete product to be formed. Each of the wall sections also has an outer wall with connecting walls spacing the outer walls from the inner walls, to form elongate spaces therebetween which are filled with insulating material. This enables the concrete to be poured in colder weather than otherwise. The wall sections also have cooperating means for enabling the inner walls to be positioned in registry and the sections have means for releasably holding them in assembled relationship when the concrete is poured. The form also preferably includes a base member which holds the lower ends of the wall sections in position and an upper collar member which helps to hold the upper ends of the wall sections in position.