is a company that sells graphite and has great DD material. Here is what they said about vein graphite:

In many applications vein graphite may offer superior performance since it has slightly higher thermal and electrical conductivity, which result from its high degree of crystalline perfection. Vein graphite also has the highest degree of cohesive integrity of all natural graphite materials. High cohesive "energy" means that vein graphite is easy to mold and can be formed into solid shapes without the aid of a binder addition.

Lot's more info on their website.

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