It’s dark, you’re cramped in a bathroom stall, and you’ve been hovering for what feels like an hour. You can feel it. That annoying, squashed-sideways sensation that tells you your menstrual cup is not opening inside. Honestly, it’s one of those "nobody told me it would be this hard" moments that makes you want to chuck the whole thing in the bin and go back to pads.
But don’t. Not yet.
The learning curve for menstrual cups is steep. Like, mountain-climbing steep. Most people take three or four cycles to actually get the hang of it, and even then, a random Tuesday will come along where the cup just refuses to pop. It stays folded. It stays flat. And then, inevitably, it leaks. This isn't usually a "you" problem or a "faulty cup" problem; it's almost always a physics problem involving suction, pelvic floor strength, and anatomy.
The Science of the "Pop"
When you insert a cup, you’re trying to create a vacuum seal against your vaginal walls. This is what prevents leaks. If the cup stays collapsed, there’s no seal. Fluid just flows right past it.
Your vaginal canal isn’t a perfect, hollow tube. It’s a muscular space that naturally stays collapsed when nothing is in it. Your pelvic floor muscles—those same ones you use to stop peeing mid-stream—are constantly putting pressure on the cup. If those muscles are particularly strong or if you’re feeling tense, they can actually squeeze the cup so hard that it can't spring back to its original shape.
Then there’s the air factor. For a cup to open, it needs to displace some air. If there’s no room for air to get around the rim as you’re pushing it up, the cup stays suctioned to itself. It’s kind of like trying to open a plastic baggie that’s wet; the sides just want to cling together.
Why Your Menstrual Cup Is Not Opening Inside Right Now
The most common culprit is often the fold you're using. If you use the "C-fold" (where you just fold the cup in half), you’re creating a very wide rim that has to fight against a lot of muscle resistance. It’s bulky. It’s stubborn.
The Punch-Down Pivot
Many enthusiasts on forums like Reddit’s r/menstrualcups swear by the punch-down fold. You push one side of the rim down into the base. This creates a much narrower point of entry. The magic happens because only a small part of the rim needs to "catch" for the rest to spring open. If the C-fold isn't working, stop using it. Seriously.
👉 See also: The Structure of the Vagina: What Your Anatomy Teacher Probably Skipped
Cervix Height and Positioning
Your cervix moves. It’s not a stationary target. During your period, it usually drops lower. If you have a low cervix and you’re trying to shove a long cup way up past it, the cup might be hitting the side of the vaginal wall or even the cervix itself, preventing it from opening. On the flip side, if you have a high cervix and a short cup, you might not be reaching the "widest" part of your canal where the cup has room to breathe.
Material Firmness
Not all silicone is created equal. Brands like Salt, DivaCup, and Saalt (which Bellabeat users often cross-reference for their wellness tracking) use different Shore hardness ratings for their silicone. A very soft cup is comfortable because it doesn't press on your bladder, but it’s a nightmare to open because it lacks "spring." A firmer cup—often marketed as "sport" versions—will pop open the second you let go, but it might feel a bit more "there" throughout the day.
Hands-On Fixes You Can Try in the Bathroom
If you're currently stuck, try the "Rotation Trick." Grab the base of the cup—not the stem, the actual textured base—and give it a full 360-degree turn. This forces the rim to move against the vaginal walls and usually clears whatever fold is caught.
If it won't turn? It’s probably caught on your pubic bone or tucked into a fold of tissue.
Try the Finger Sweep.
Insert one finger and run it all the way around the rim. You're looking for any indentations. If you feel a flat spot, gently press the vaginal wall away from the cup. This creates a tiny gap for air to rush in, which usually provides the pressure needed to "pop" the silicone outward.
Sometimes the issue is actually the tiny air holes near the rim. These are not there for decoration. They break the vacuum seal when you’re removing the cup, but they also help it open during insertion. If they are clogged with... well, period blood... the cup won't open. Make sure those holes are pin-clean every single time you boil or wash it.
The Squat, the Lean, and the Leg-Up
Your posture matters. If you’re sitting on the toilet with your knees together, you’re tightening your pelvic floor. That’s the opposite of what you want.
Try this:
- The Captain Morgan: Put one foot up on the edge of the bathtub or the toilet lid. This opens up the pelvis.
- The Deep Squat: Get low. Like, "camping in the woods" low. This shortens the vaginal canal and makes it easier to reach the rim to ensure it’s open.
- The Bear Down: Gently push with your abdominal muscles (like you're having a bowel movement) while you’re inserting. This pushes the vaginal walls out slightly and can give the cup the millisecond of space it needs to snap into shape.
When to Admit the Cup is the Wrong Fit
Sometimes, your menstrual cup is not opening inside because it’s literally the wrong size or shape for your body.
If you’ve had a vaginal birth, your vaginal canal might be slightly wider, meaning a "Size 1" or "Small" cup doesn't have enough surface tension to stay open. It just flops. Conversely, if you have very strong "hypertonic" pelvic floor muscles (common in athletes and pilates enthusiasts), you might be crushing a soft cup.
Check your anatomy. Use a clean finger to find your cervix. If it’s easy to find (about one knuckle in), you need a short, wider cup. If you can’t reach it at all, you need a long, firm cup. Using a cup that doesn't match your cervix height is a recipe for constant frustration.
The "Water" Hack
Dry silicone on dry skin is like trying to slide a rubber eraser across a desk. It sticks. It drags. It bunches up.
Always rinse your cup with cold water right before insertion. Leave it wet. The water acts as a natural lubricant. If that’s still not working, use a tiny drop of water-based lubricant only on the rim. Do not use oil-based lubes; they will degrade the silicone over time and make the cup cloudy and gross.
Actionable Steps for Your Next Cycle
Don't wait until you're at work or in a rush to fix this. It’s too stressful.
👉 See also: Isotroin Before and After: What Your Dermatologist Might Not Tell You
- Practice in the shower. The warm water relaxes your muscles, and you don't have to worry about a mess. It's the best place to experiment with the 7-fold or the Origami fold.
- Verify the seal. Once you think it's open, give the stem a light tug. If you feel resistance/suction, you’re good. If it slides right out, it’s not open.
- Check the air holes. Use a toothpick or a dedicated small brush to ensure the four tiny holes at the top are completely clear.
- Consider a Disc. If you’ve tried three different cups and they all refuse to open, look into menstrual discs. They don't rely on suction or "popping open" in the same way. They tuck behind the pubic bone and are often much easier for people with high muscle tone.
- Track your symptoms. Use your Bellabeat or other wellness trackers to note when the cup is most difficult. Many find their cervix is much lower and their muscles more sensitive on Day 1 versus Day 4.
If you can feel the rim and it’s still flat, take it out, take a deep breath, and try again. Sometimes the third time really is the charm. Just remember that your body isn't "broken"—it's just a matter of matching the right folding technique to your unique internal landscape. Once you find the "sweet spot" where the cup clicks open, you’ll never want to go back to disposables again.