What is the vaginal fornix?

The low-key superstar of vaginal anatomy

The vaginal fornix may not have made it into your high school anatomy textbook, but in our eyes, it’s the real MVP. Here’s what you should know: 

The vaginal fornix – or fornices – is the widest part at the end of the vaginal canal, forming a dome shape around the cervix. (Hint: This is where the Flex Disc sits for up to 12 hours at a time while you’re on your period.)

The opening of the cervix is shaped a little bit like a donut (if that donut had a really, really small hole): The area around the cervical opening protrudes forward slightly into the vaginal canal. The space that exists between the opening of the cervix and the wider back “wall” of the vaginal canal is what makes up the vaginal fornix.1 

For a better understanding of what this space looks and feels like, try puckering your lips like you’re going in for a very exaggerated peck. Wrap your pointer finger and thumb around your lips, one on top and one on the bottom, as if you were making an “okay” symbol with that hand. That weird shape you just created is (more or less) what the vaginal fornix looks like if you were to peer up your own vagina with a flashlight.

The vaginal fornix during sex

Sometimes, the vaginal fornix is referred to in two parts: the anterior vaginal fornix (in the front) and the posterior vaginal fornix (towards the back). The posterior fornix is shaped in a way that’s conducive to, well, getting you pregnant: Its pocket-like shape allows your body to catch and retain ejaculated semen at the back of the vagina.2 

The semen can hang out in the posterior fornix for up to 20-30 minutes, after which it liquefies. This makes it easier for semen to be absorbed into the cervical canal. 3

If you love period sex but hate dealing with stained sheets, your vaginal fornix might just be your new favorite body part. You can have mess-free period sex by popping in a Flex Disc before getting busy. Thanks to your fornix (and a little help from your pubic bone), the disc stays secure in any position. 

During period sex, the Flex Disc may even intensify orgasms by rubbing up gently against the cervix. Your average clitoral orgasm is typically centered around the vagina, with sensations that last only last a few seconds. When the cervix is stimulated, however, the pressure can build up and result in full-body orgasms that may last longer than usual.4 The vaginal fornix is the little space that makes this all possible.

We’ve been asked a few times if the Flex Disc can be used in place of birth control. It is important to emphasize that Flex is not a contraceptive, but it’s safe to use with other forms of contraception.

The vaginal fornix & period protection

When it comes to period protection, the Flex Disc is designed to sit in the vaginal fornix. We recommend inserting the disc down and back, pushing the medical-grade polymer rim all the way into the posterior fornix (it feels like it’s going really far back, but it can’t get lost!). 

Once the back is secured, the front of the disc finds its rightful place along the front-facing side of the vaginal canal. Your pubic bone acts like a retaining wall or a ledge, holding the disc snugly in place around your cervix. 

Tip: You’ll know it’s in the right position when you can’t feel anything. 


Helena shows us how the Flex Disc is inserted into the vaginal fornix with a 3D model.

Even though no one really talks about the vaginal fornix, we’re here to sing its praises. This small but mighty vaginal space allowed us to create products that help us bleed easier every month. Stress- and mess-free periods, brought to you by the fornix and its trusty sidekick, the Flex Disc.

Had you ever heard of the vaginal fornix before? Have questions about the role it plays during sex, orgasm, or your period? Write to us at thefornix@flexfits.com

A diagram showing the vaginal fornix within the female reproductive system.