https://cultpens.com/products/exacompta-white-5-x-3-125-x-75-record-cards-pack-of-100

These are surprisingly inexpensive here at CultPens.com! They don't seem to have the larger 100x150s though.

At 9¢/card these are very expensive in comparison to bulk cards which usually can be found for 1-2¢/card. The difference however is in the luxuriousness of the silky smooth texture. Whether you're writing with your favorite fountain pen or a carefully chosen pencil. I don't know if these are the same brand of Bristol cards that Vladimir Nabokov used for his writing, but one could easily image him using such lovely material.

These provide a very smooth writing experience for fountain pens, gel pens and pencils. I particularly love the way my Tennessee Reds and Blackwing 602s glide over their surface. In comparison to some Japanese stationery, I'd put these cards somewhere between tsuru tsuru (slippery) and sara sara (smooth). If you're looking for a toothier paper, you'll definitely want to look elsewhere. They take fountain pens pretty well with no feathering or ghosting. My juiciest fountain pen dries in about 15 seconds, while a drier extra fine is dry in about 7 seconds, so it may take some care not to smear ink if you're on the messier end of the spectrum.

Pencil erases reasonably well, though there may be some minimal residual ghosting here. At 205 gsm, they've got a satisfying thickness unseen in most index cards and one is unlikely to rip or crinkle them when erasing. They're also thick enough that the wettest Sharpie won't bleed much less ghost through. You have to hold a card up to a backlight to see the appearance of any ghosting through it and even then, not well.

For the sticklers used to using standard 4 x 6" index cards, one should take note that the dimensions of these are slightly shorter in both dimensions—they're closer to 3.94" x 5.91". This means that you might have to take some care that while flipping through mixed company of cards your Exacompta can potentially hide between larger imperial sized cards. They're also close to, but not quite A6 in size either (105 x 148.5 mm or 4.1 x 5.8 inches).

https://www.paperbistro.com/browse-by-brand/exacompta/paper/index-cards.html

Manufacturer direct

https://www.exaclair.com/

I should mention that the Stockroom Plus 4 x 6" cards I got a while back are great with even my juiciest fountain pens. They're some of the least expensive gridded cards I've been able to find and are a fraction of the cost of the Exacompta.

u/abbienormal, u/Alan_Shutko, u/CynTut all recommend Exacompta cards for fountain pen friendly use.

4x6": - Goulet Pens - White Graph $9.00 - White lined $9.00 - White blank $9.00 - Pastel graph $13.50 - Flotsam and Fork Pastel graph $9.50 - Anderson Pens $13.50 (multi-color) - JetPens Pastel graph $14.50 - Amazon White(?) grid $19.96

• Kokuyo
  • may be close in size but A or B style sizing

https://www.flotsamandfork.com/collections/new/products/exacompta-heavyweight-index-cards?variant=39534626340963

is flexible, but I am rather particular about my instruments: lined Bristol cards and well sharpened, not too hard, pencils capped with erasers.

Nabokov on his system of writing.