Oxygen Free Copper:
< RANT >
As you have probably noticed, wire designated as OFC wire usually has a clear insulation and the wire is bright and shiny underneath the transparent insulator. Well... It is nice and shiny for a while but after a short time (actually from the time it is drawn), it starts to oxidize (unless the wire is kept in an oxygen free atmosphere). When copper oxidizes, it becomes a less effective conductor. This means that, in time, the wire's current carrying capabilities will become significantly reduced. The problem is made worse by having many very small conductors. This creates even more surface area which makes the oxidation process even more efficient. In my opinion, if you are designing a system of any type for long term use, I think the better choice is a 'tinned' copper wire. In this type of wire, the copper is plated with tin (maybe a lead/tin alloy) or similar conductor which will not oxidize as quickly and never as completely as the bare copper. As a side note, this has nothing to do with the copper being 'oxygen free'. It has everything to do with the fact that the wire is unprotected (untinned) and is finely stranded. I used OFC wire in this example because most OFC has many fine unprotected strands.
< /RANT >