There must be some differences in deformation characteristics between thin- and thick-walled tubes in tube forming. Experimental results using copper tubing of 8 mm outer diameter (D) are discussed. 0.5- and 0.8-mm-thick specimens were used in cross-shaped-tube hydroforming. Long protruding branches were formed under a constant fluid pressure range and a relatively large amount of axial feeding of approximately 4D. It was revealed that the 0.8-mm-thick specimens have a wider range of faultless forming conditions than the 0.5-mm-thick ones. It seems that there is a thickness threshold between 0.8 mm (0.10 D) and 0.5 mm (0.06 D). In addition, the conditions for contact between the tubular specimen and the die strongly affected the forming results. A MoS₂ spray and PTFE sheets were used as lubricants to examine the effects of friction on axial feeding force and tube deformation. The highest axial feeding force was recorded under the forming condition of the 0.8-mm-thick tubing and MoS₂ spray without PTFE sheets. Forming pressure had a small effect on feeding force. The length of the formed branches depended on forming pressure and the type of lubrication.