It is card stock - - really what could go wrong with card stock. I use it mostly in my wonderful HP printer and I have had no problems. The colors are vibrant and cheerful. i wish they had some more muted colors to choose from but these work.
I actually purchased this by accident however it came in great for our Kindergarten teachers. They will be using it for sight words for the children to practice.
It's great for teachers researchers....You canpunch holes in the card stock paper and use as dividers by themselves to separate articles or papers. Can be added to use within the plastic Dividers. Colors help to organize "color code" sections. They are excellent!