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C101 vs C102: When the Purity Grade Matters

September 26, 2026

Two grades, both called oxygen free copper, both around 101 percent IACS, both machining identically. Buyers ask whether the difference is real. It is, but it is not where most people look for it.

What is actually different

C10100, OFE, oxygen free electronic. Minimum 99.99 percent copper, with tight limits on a defined list of residual elements and a very low oxygen content. Produced and certified under controlled conditions for applications where purity is measured.

C10200, OF, oxygen free. Minimum 99.95 percent copper, oxygen free without the same tight residual element control.

That is the whole difference. One is a purity and certification grade, the other is oxygen free copper without the paperwork.

	C10100 OFE	C10200 OF
Copper minimum	99.99 percent	99.95 percent
Oxygen	Very low, controlled	Low
Residual element limits	Specified	Less restrictive
Conductivity	About 101 percent IACS	About 101 percent IACS
Machinability	20	20
Hydrogen embrittlement	Resistant	Resistant
Typical use	UHV, accelerator, hydrogen brazed, certified	General oxygen free work

Published typical values, not a promise from any shop.

When the difference matters

Ultra high vacuum and accelerator components. Outgassing and inclusion behaviour are what you are paying for, and the specification will name C10100. Do not accept a substitution.

Certified conductivity or purity. If a certificate has to show the residual element limits, only C10100 carries them.

Hydrogen brazing. Both are oxygen free and both resist hydrogen embrittlement. Either works for that property alone, and the drawing decides which by naming it.

Anything where the buyer’s own specification says C10100. Then it is C10100, because a substitution is a nonconformance whether or not it would have performed.

When it does not

For an oxygen free part where nobody is measuring outgassing or residual elements, C10200 does the same job, is often easier to source and may be cheaper. This covers a surprising amount of work that is specified C10100 out of habit.

The trap

Stockists and some shops quote the two as interchangeable, and in most applications they are. The trap is a drawing that says C10100, a shop that buys C10200 because it is on the shelf, and a certificate that says C10200 at first article. That is a rejected part even though it would have worked.

The fix is one line on the drawing. Either “C10100, no substitution” or “C10100 or C10200 acceptable”. Silence gets you whichever bar was closest.

What to write

Oxygen free electronic copper, UNS C10100,
ASTM B187, temper O61. No substitution.
Material certificate EN 10204 3.1 required.

Or, when the purity level is not itself a requirement:

Oxygen free copper, UNS C10200 or C10100,
ASTM B187, temper O61.

Reference pages: C10100 and C10200. The vacuum rules that usually drive the choice are in oxygen free copper for vacuum and UHV, and reading the certificate is covered in copper material certificates.

Frequently asked questions

Keep reading

• C18150 vs C18200: Which Chromium Copper to Put on the Drawing
• C14700 Sulfur Copper: What It Gains Over C110 and Where It Stops