The Clairefontaine Twinbook is a new product to 2010, something unique but familiar. There is nothing in the Twinbook that's 'revolutionary', just very, very practical. There is a blue sticker on the cover as you see in the pic, but it's easily removable.
Twinbooks are essentially Clairefontaine Staplebound notebooks with grid paper, and a cutout breaking the pages into two distinct sections. No frills, it just works.
The Twinbook comes in two sizes, a smaller size A5 (6.75"x8.625") in the C63642 that's a list price of $3.50, and a larger size A4 (8.25"x11") in the C63612 with a list price of $6.50.
Both sizes of notebooks have the same type of paper and same sheet count, 48 sheets (96 pages). The paper in them is 90g, smooth Clairefontaine paper exactly like what you know in the other Clairefontaine notebooks. The only difference is the ruling! Many of the Clairefontaine notebooks with grid (graph) ruling in the past have been 10x10 (10mm square). But these Twinbooks have 5x5 grid ruling that's the same size as the Rhodia grids. I had to think about it for a second, but I'm actually realizing now that all of the Clairefontaine products that Exaclair is importing into the US have the 5x5 grids instead of the 10x10. Good call!
I tested the paper with 3 different inks and pens. All performed wonderfully (as you might expect from Clairefontaine), with absolutely no feathering, no bleedthrough, and very, very little echo (aka ghosting, show-through).
Clairefontaine Twinbooks are available in two sizes, A5 for $3.25 and A4 for $6.25 at the Goulet Pen Company.
Link to YouTube for iPhones and full-screen viewing.