It's plastic filled with plaster or some other weight. I couldn't understand from the image or description what it actually was. The actual unit doesn't have as much metallic airbrushing on it so it looks more plasticy. Still, it's more aesthetic than the bulkier units that get filled with water. Since the umbrella will be used only in a table and never standalone, this works well.

Very sturdy and has withstand thru the last winter. Hopefully will last for more years.

Used this summer and looks very sturdy. Hope it won’t get brittle over the winter.

arrived well but not tried yet. I'll write back if anything

This base holds 9-feet umbrella in windy days without problems. We occasionally have strong winds in the area, strong enough to slide a relatively heavy glass table on the deck, blow chairs off the deck. Once I receive the base and 9-feet umbrella, I set them go through the eyelet in centre of the table. This base keeps both the umbrella and the table in place.

Good