Aluminium on synthetic core.
4 out of 5 found the following review helpful
Pros: A nice warm sound, but with good clarity. I find it hard to get a good over-all balance of sound on my 'cello, and have spent a lot of time and money trying different string combinations. This Aricore gives me the sound that I want and 'speaks' easily. Many strings seem to fall into the category of 'harsh', or 'woolly'....this one seems to avoid both extremes.
Cons: It took a while to settle and stay in tune. I would be would be a bit aprehensive about having to put on a new one in the middle of a concert.