Kt by Knix, a sister company to the intimates and apparel brand Knix that focuses on kids and teens, has published a book to destigmatize a moment every young girl faces: the onset of her first period.

The book, titled Some Periods, was written by Knix’s founder and president, Joanna Griffiths, and inspired by her own experiences as a child. “It’s a book I wish I had growing up,” she explains.

“This book was born out of a desire to avoid shying away from talking about periods. When we shy away, we send the message that periods are shameful or gross,” adds Emily Scarlett, director of communications for the brand. “Kt by Knix intends to end the confusion, embarrassment and misinformation and use this book to empower people to bleed with confidence.”

The book launched on Sept. 7 alongside a $5,000 donation to non-profit I Support the Girls, which donates bras and menstrual products to those in need. It also shared the book with the larger Knix community and “friends of the brand,” says Scarlett, to “spread the importance of educating children about their bodies at a young age.”

Back-to-school season was “the perfect time to share new educational content,” she adds, noting that the community must have agreed, since the $13 book (of which there were 100 copies) sold out on the first day of launch, and the brand has plans to restock it.

“Knix’s brand mission is to inspire our community to live unapologetically free,” Scarlett says. “Some Periods, from our sister brand Kt by Knix, mirrors just that. Educating youth about their bodies, how they work and preparing them for puberty is imperative to them understanding how their bodies will work as adults without any shame or discomfort.”