They are traditionally handmade in India, using recycled cotton rag. They are a nice weight, 210gsm, and the ones I chose are 150mm square. They had A6 and mini size too. And the paper has a fabulous texture and finish.
There isn't a weight spec for the paper. And if I tried to guess I'm likely to be totally wrong. So I won't. But it's a little lighter in weight than the card blanks.
They cost me a little more than I would usually pay for card blanks and paper - a pack of 5 cards with matching envelopes cost me £5.00. But they are a little bit different, and they print beautifully.
And I think they're my new favourite : )