The Copic Bleedproof Marker Pad here is made in Italy. It comes in three sizes: A4, A3 and A2. Each pad comes with 50 sheets of smooth white paper.
The paper is 70gsm, just about as thick as typical copier paper. They don't really have to be that thick because the paper is alcohol based and treated to prevent ink bleeding through the opposite side.
They are also thin enough to be used for tracing. Useful if you require that.
Here's a quick sketch I did. It was drawn with pencil before inking with the 0.8 Copic Multiliner pen - which works very well on it. Then I erased the pencil lines which didn't cause any fading to the black lines. The pencils won't come off after marker ink is applied over them.
I usually use my Copic markers on sketchpads with higher absorbency. Comparatively speaking, light colours seem to have a tendency to be lighter on the marker pad because there's no soaking through. When I first applied the skin tone colour, I thought my marker dried out.
The paper can take on multiple coats of ink. On the left are three coats of 100 Black applied with the wide marker. Technique must be right to achieve flat colours with the smaller broad tip markers. My technique for the jeans is a bad example.
I also tried a bit of watercolour and the area buckled quickly with the water. Definitely not suitable for watercolour.
The best paper for Copic? I guess this marker pad would be more suitable for professionals designers and architects. For casual sketches, I'll go with sketchpads with a bit more absorbency because of the issue with lighter colours.