After getting back into coloring over the past summer; and going several Facebook groups about adult coloring; I have asked a lot of questions on what is a better medium to use in the adult coloring books and of course there is some mixed reviews or preferences; but I am very pleased with my purchase and I haven't had any problems with it. It all depends on the quality of the paper, thickness, and if the coloring book is single sides or double sided if I would trust markers in it. These so far I haven't had any problems on single sided coloring books with these; double sided; I would trust them though; like in Johanna's books the Secret Garden and her other books.