It's either split cane or rattan....can't tell without a closer look....b ut they are very much they same.

Suspect it's resin wicker, but can't really tell by the photograph. I used to do floral wedding designs, and purchased wicker fern and plant stands to be used both inside and out of doors. They were made of resin wicker, and the material looks very much like that in your chair. It's a synthetic plastic composition and that would answer why after you filed it, all you could see is more white. Often furniture made of it is supported by an aluminum frame.

I realized after looking at the chair again that I left out some important information. The strips from which this is made are highly stressed - they almost ring when tapped, so the chair is extremely rigid. Also, there is a smooth, white coating over everything that is harder than paint. Also, there is not a single exposed end!

I have added some closeup pictures at the link below. Note the irregular surface (rough was a poor description) of the arm in the first pic, which apparently is from weaving the material together. In the second pic one can see what appear to be brush marks. I know the stain by the hole look like rust, but I rechecked the frame with a strong magnet and there is no attraction.

I also missed pointing out previously that the holes I mentioned occur at every intersection of strips to the outer structure, probably some sort of bracing point during assembly. You can clearly see that in the 3rd pic, which also shows the heavy application of a coating.

I have the impression this was possibly a one-off piece, as it is so unique does not have a manufactured look, and would have been extremely labor intensive to make. At the same time it's a huge undertaking to design for one piece, and I would think an exhibition piece would have been even more finely finished.

Here is a link that might be useful: Mystery Chair

I think Calliope is right....looks like resin.

We see this type of patio furniture often here (FL). Below is a link to a set currently available on craigslist. I have to say that the one in the link is priced way too high, compared to other sets of the same type.

Here is a link that might be useful: Resin wicker patio set

SOLVED! - It's made of spun fiberglass, which make sense considering it it both light and strong, and now that I look even closser I see the "fibers" are not flat like real or fake rattan/wicker, but rather more round or square in cross section. It's so heavily coated that I did not realize that the strands themselves were woven. Also makes sense for the arms, which are probably strips of fiberglass fabric. Here are pics of almost identical items. http://www.1stdibs.com/furniture_item_detail.php?id=452811