Determine the size of the portable wall. Measure the space in which the wall will be used, and record the numbers.
Cut four 2-by-4-inch pieces of pine lumber to the dimensions you measured. To make a portable wall that is lighter, use 2-by-2-inch pine lumber. Pine is a very lightweight lumber.
Lay the four pieces of lumber on the floor so they form a frame. Each 2-by-4 should lay flat on the floor with the long lengths outside the short lengths. Use a power drill to insert carpentry screws into the ends of the frame.
Cut foam board insulation with a utility knife to the length and width of the inside of the frame. Because the foam needs to fit tightly inside the frame, cut it a little larger than you think it should be at first, and then reduce its size as needed.
Coat the inside of the frame with hot glue from a hot-glue gun, and then set the foam board inside the frame. Use clamps on the wood part of the frame and the foam to hold the foam in place. Allow the glue to dry completely.
Decorate or finish the portable wall with paint or fabric as desired.