Joshua Roth 2.5 mm anodized aluminum wire oxidizes to a lesser degree than copper, and is easier to conform to your preferred contour. 

Its dark brown color blends well with Bonsai branches to create a more natural appearance.

The gauge of wire needed depends on the strength of the Bonsai branch. It is generally recommended to use wire that equals 1/3 the thickness (diameter) of the branch being shaped, although branch strength does vary between species and individual Bonsai trees.

Multiple wire strands may be used if needed. Cut wire about 50% longer than the branch you are shaping. To remove, use wire cutters to prevent damage to leaves and branches.

JR 2182.5 wire specifications:

Applicable branch thickness = 7.5 mm
Wire diameter = 2.5 mm
Wire length = 36'
Total wire weight = 150 g