When you ask someone what license they are using for their open source hardware project, you’re quite likely to hear the answer “Creative Commons.” And unfortunately, that doesn’t fully answer the question.
The reason is that there is not a single entity called the “Creative Commons license.” Rather, Creative Commons offers a number of different licenses that can apply some rights and protections to your work, including the CC-BY and CC-BY-SA licenses which reflect open source values closely. In the 2012 and 2013 surveys these licenses were, in fact, the most popular licenses used for open source hardware documentation. (Creative Commons licenses cannot be applied to the hardware itself.)
Creative Commons also offers licenses that carry restrictions — against commercial use and/or derivative works — that are strictly incompatible with open source¹. The open source hardware definition states that a license for open source hardware “[…] shall allow for the manufacture, sale, distribution, and use of products created from the design files, the design files themselves, and derivatives thereof.” Thus, if you choose to release hardware under the banner of “open source,” that means that you agree to allow others to use your design commercially, as well as to create derivative works (and to use them commercially). Consequently, you cannot advertise your project or product as “open source” if it carries restrictions against either of those uses.
To enumerate the particulars, the following licenses are compatible with open source:
Creative Commons Attribution (CC BY)
Creative Commons Attribution-ShareAlike (CC BY-SA)
While the following licenses carry restrictions that are not compatible with open source:
Creative Commons Attribution-NoDerivs (CC BY-ND)
Creative Commons Attribution-NonCommercial (CC BY-NC)
Creative Commons Attribution-NonCommercial-NoDerivatives (CC BY-NC-ND)
Creative Commons Attribution-NonCommercial-ShareAlike (CC BY-NC-SA)
¹The Open Source Hardware Definition itself is a derivative work of the Open Source Definition (for software), and its language regarding commercial use and derivatives of OSHW is directly adapted from the language in the software context. Restrictions against commercial use and/or derivative works are incompatible with open source hardware, and also incompatible with open source software.