PURPOSE: To improve productivity of a tube material for a heat exchanger of which the heat exchange efficiency is excellent, by a method wherein holes making adjacent chambers communicate with each other are provided in each partition wall and the respective communication holes of at least two or more partition walls are provided in a state of being asymmetric mutually on the right and the left, in the direction of the length of the tube.

CONSTITUTION: A tube material 1 is a flat tube material. Inside a hollow part, three partition walls 2, 3 and 4 are disposed in the width direction and provided respectively with communication holes 2a, 3a and 4a, through which adjacent chambers 6 are made to communicate with each other. When the communication holes 3a provided in the partition wall 3 positioned in the center are compared with the communication holes 2a and 4a provided in the partition walls 2 and 4 positioned on the right and the left, the holes 3a, 2a and 4a are formed in a state of being asymmetric on the right and the left wherein they are different in the size of the hole, though identical in the number thereof for a unit length, in the direction of the length of a tube.