It’s 3:00 AM. You wake up with that familiar, nagging dread, wondering if you’re about to ruin another set of expensive sheets. Most of us have been there. It’s a specific kind of stress that only happens once a month. You’ve tried doubling up, you’ve tried the "thick" pads that feel like wearing a literal diaper, and yet, somehow, leaks still happen. This is exactly where Always Flex Foam Size 4 comes into the picture, and honestly, it’s a bit of a weird product if you really look at the science behind it.
It doesn't feel like cotton. It doesn't act like paper. It’s a dense, flexible foam that was originally developed in a lab to behave more like a sponge than a traditional sanitary napkin.
What is FlexFoam anyway?
Most pads are basically just fluffed-up wood pulp. They’re designed to trap liquid in the center, but once they get wet, they get heavy. They bunch up. They lose their shape. FlexFoam is different because it's a liquid-turned-foam structure. P&G spent years perfecting this material to ensure it could absorb ten times its weight while remaining incredibly thin. When you pick up a box of Always Flex Foam Size 4, you’ll notice it feels almost empty. It’s light.
That lightness is deceptive.
The "Size 4" designation is specifically for overnight use or for those with a very heavy flow during the day. It’s longer than your standard pad—about 13 inches, give or take—and it flares out at the back. That back flare is the hero of the story. If you’re a back sleeper, you know that gravity is your worst enemy. The liquid travels. By having that extra width at the tail end, the Size 4 catches what other pads miss.
The weird physics of how Always Flex Foam Size 4 works
You’ll notice tiny holes on the top layer. These aren't just for decoration. They are micro-holes designed to pull liquid away from the surface and tuck it into the bottom layer of the foam. This keeps the top feeling dry against your skin. Nobody likes that "wet" feeling. It’s gross. It causes irritation. By moving the moisture to the bottom of the pad, FlexFoam keeps the surface surprisingly crisp.
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Is it perfect? No.
Some people find the foam texture a bit "plastic-y" at first. It makes a slight crinkling sound when you first take it out of the wrapper, though that usually stops once it warms up to your body temperature. But the tradeoff is the flexibility. Because it’s foam, it moves with you. If you’re tossing and turning in bed, the pad doesn't just fold over and create a gap. It twists. It recovers its shape.
Sizing matters more than you think
Always uses a "MyFit" system, which is basically a grid based on your panty size and your flow level. Size 4 is the sweet spot for heavy flow. If you’re wearing a size small undie but have a heavy flow, you still want the Size 4 for the length. If you’re wearing a larger size, the Size 4 provides the coverage area you need to prevent side-leaks.
- Size 1: Regular (Yellow)
- Size 2: Heavy (Green)
- Size 3: Extra Heavy (Blue)
- Size 4: Overnight (Orange/Red)
- Size 5: Extra Heavy Overnight (Purple)
The Size 4 is the workhorse of the lineup. It's the one people grab when they're tired of checking their pants every twenty minutes.
Why the "foam" part isn't just marketing hype
A lot of period products claim to be "revolutionary," which usually just means they changed the scent or the pattern on the wrapper. But FlexFoam actually changed the chemistry. Traditional pads use "Super Absorbent Polymers" (SAP) mixed with fluff. When SAP gets wet, it turns into a gel. That gel gets squishy. If you sit down hard, that liquid can sometimes be squeezed back out—a phenomenon known as "rewet."
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FlexFoam doesn't do that. The cellular structure of the foam holds the liquid in place through capillary action. You can sit, jump, or sleep on your side, and the liquid stays locked in the lower cells. This is why Always Flex Foam Size 4 is often recommended for postpartum use as well. After having a baby, the flow is unpredictable and heavy. You need something that won't fail when you finally get two hours of sleep.
Real talk: The downsides
We have to be honest here. FlexFoam isn't the cheapest option on the shelf. You’re going to pay a premium for the technology. If you’re on a strict budget, the "Yellow Box" Always Maxi pads are way more affordable, but you’re sacrificing that thinness and the dry-top feel.
Also, the wings. The wings on the Size 4 are quite large. While this is great for security, if you're wearing very narrow-gusset underwear (like a lace thong—though why you'd wear that with a Size 4 is a mystery), the wings might overlap too much or feel bulky. These are designed for full-coverage cotton briefs. They need a solid foundation to stick to.
Breaking down the "unscented" debate
Always offers these in scented and unscented versions. Generally, experts and gynecologists suggest sticking to the unscented ones. Fragrances in period products can mess with your pH balance. The Size 4 FlexFoam does a decent job of masking odors naturally because it pulls the moisture away from the air, so you really don't need the added "fresh scent" chemicals.
How to get the most out of your Size 4 pads
It sounds simple, but most people put their pads on incorrectly. For the Size 4, placement is everything. Since it's an overnight pad, you want to position it slightly further back in your underwear than you would a daytime pad. This accounts for the way liquid moves when you're lying flat.
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- Peel the backing off the main body first.
- Center the narrow part of the pad with the front of your underwear.
- Secure the back flare so it covers the entire rear area.
- Only then, wrap the wings around the center.
If you do the wings first, you might misalign the length.
Actionable Steps for Better Cycles
If you're currently struggling with leaks or discomfort, here is how to transition effectively.
Audit your current supply. Look at what you're using. If you are changing your pad more than every 3-4 hours because it feels "full" or "wet," you need to move up a size or switch to FlexFoam.
Track your flow patterns. Use an app or a simple notebook. Note which nights you leak. If it’s always the first two nights, reserve your Always Flex Foam Size 4 specifically for those "high-risk" windows to save money while maintaining total security.
Check your underwear fit. A pad is only as good as the fabric it's stuck to. If your pajamas are loose, the pad will move. Wear snug-fitting cotton underwear during your heavy nights to ensure the FlexFoam stays flush against your body.
Compare the cost per unit. Don't just look at the box price. Check the "price per pad." Often, the larger "Club Packs" at stores like Costco or through Amazon subscriptions drop the price of FlexFoam down to nearly the same price as the standard thick pads.
The reality of period care is that one size never fits all, but the Size 4 is about as close as it gets for anyone dealing with a heavy flow. It’s thin enough to ignore but strong enough to trust. No more ruined sheets. No more 3:00 AM laundry sessions. Just a bit of science helping you get through the week.