We sell these cards because they’re really useful for recording things but have also found a lot of people look for them to design their own games. Other people have used them for school projects, as flash cards and for replacing lost or damaged cards from other games.
These matte cards are blank on BOTH sides and (as you can probably see from the image) have a paper-like finish with a very thin coating for durability. They are 57mm x 88mm in size (the typical size of most playing cards).
You can write on these with most pens and pencils very easily. Heavy-ink pens (like Sharpie pens, or whiteboard pens) may bleed slightly after writing, like they would on normal paper.