Our notebooks are filled with some of the highest-quality 100% recycled paper on the market. (It's also acid-free and 100% post-consumer waste!) Most of our notebooks (Hypothesis, Experiment, Analysis, Observation, Abstract, Research) are filled with an 81 gsm paper, which is perfect for journaling and taking notes, while The Theory series has a thicker, sturdier 128 gsm stock that's great for sketching, notes, and slightly wetter mediums. 

81 gsm:

The paper does well with fine and ultra-fine nibbed fountain pens, although we don't recommend super wet mediums or wide nibbed fountain pens.

We found that there is some slight feathering (particularly if the ink is on the wetter side), a fast dry time, and very little show-through using a fine or ultra-fine nib fountain pen. Wide and extra-wide nibs, particularly calligraphy-style pens and wet markers/Sharpies that produce larges strokes of ink do have some show-though. You can see photos of this test below.

81 gsm paper pen test:

Here is the new paper with some more traditional writing tools; gel pen, ballpoint pen, different colors of flare pens, and highlighter.

There's no feathering at all with any of these, and the only real show-through came from a brand new Sharpie and green highlighter.

128 gsm:

The 128 gsm paper found in The Theory can handle some water pens and pencils (we still don't recommend you cover the whole page all at once), some calligraphy pens, and brush pens. There is still some light feathering that happens with certain fountain pens, and wide-nibbed pens will have some show-through.

128 gsm pen tests:

This was painted in watercolor. You can see there's a slight bend in the paper, but overall it holds up to light water mediums.

Feel free to reach out to us with any additional questions! Happy journaling!