You've probably seen them everywhere. The double-strap silhouette is basically a uniform at this point, but there’s something oddly specific about the Birkenstock Arizona mocha size 40 that makes it a constant sell-out risk. It’s not just a random shoe size or a generic brown color. Honestly, it’s the intersection of the most common European foot measurement and a colorway that hides dirt better than almost anything else in the lineup. If you’re hunting for this exact pair, you’re likely dealing with the "Goldilocks" of footwear—everyone wants it, and for good reason.
Birkenstock has been around since 1774, which is wild when you think about it. Johann Adam Birkenstock started as a "subject and shoemaker" in a small German village, but the Arizona model we know and love didn't actually hit the scene until 1973. Since then, it’s gone from "ugly" orthopaedic gear to high-fashion runways.
The Size 40 Dilemma and Why It Vanishes
Let’s talk about that size 40. In the world of Birkenstock, a 40 translates roughly to a women’s 9-9.5 or a men’s 7-7.5 in the US. It’s the ultimate "pivot" size. Because it sits right in the middle of the bell curve for both men and women, the inventory for a Birkenstock Arizona mocha size 40 gets hit from both sides of the gender aisle. You’re competing with everyone.
I’ve seen people try to size up to a 41 or down to a 39 just because they’re desperate for the mocha finish. Don't do that. Birkenstocks aren't like sneakers where you can just lace them tighter. If the arch support—which they call the "medial longitudinal arch"—doesn't align with your foot, you're basically paying money to have a piece of cork stab you in the soul for three months. A size 40 has a specific footbed length of roughly 260mm. If your foot is 255mm, you're golden. If it's 265mm, your toes will hit that front lip, and it’ll drive you crazy.
Why Mocha Beats Black and Stone Every Time
Colors matter. A lot. While the "Stone" color is popular, it shows water spots if you so much as look at a puddle. Black is classic, sure, but it can look a bit harsh against pale skin or certain summer fabrics. Mocha is the workhorse. It’s a rich, matte brown that uses Birko-Flor or nubuck leather to create a neutral base that works with denim, linen, or even workout gear.
Birko-Flor is a synthetic alternative that Birkenstock developed. It’s got a soft fleece lining. If you’re looking at the Birkenstock Arizona mocha size 40 in the leather version, you're getting something that ages and patinas. If you go Birko-Flor, it stays looking new longer but doesn't breathe quite as well. Most people buying the mocha version are looking for that "earthy" vibe that doesn't scream "I just bought these yesterday." It has an immediate broken-in look.
The Footbed: Regular vs. Soft
This is where people get tripped up. You'll see two versions of the mocha 40. One has a blue logo on the footbed, and the other has a yellow/gold one.
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- The Classic Footbed (Yellow/Gold Logo): This is the OG. It's firm. It takes about two weeks of "this kind of hurts" before it becomes the most comfortable thing you've ever owned.
- The Soft Footbed (Blue Logo): This has an extra layer of foam. It feels better the second you put it on in the store.
Here’s the thing though: purists will tell you the classic footbed is better for long-term foot health. The soft footbed is great, but that extra foam layer slightly reduces the depth of the heel cup. If you have high arches, stick to the classic. If you have sensitive soles or "bony" feet, the soft footbed in a Birkenstock Arizona mocha size 40 is a lifesaver.
Breaking Down the Birko-Flor vs. Leather Argument
The mocha colorway is most commonly found in Birko-Flor. People sometimes feel "cheated" buying synthetic, but honestly, for a size 40 Arizona, Birko-Flor is often more practical. It’s tear-resistant, easy to clean with a damp cloth, and way cheaper than the high-end oiled leather.
The oiled leather mocha is a different beast. It’s thicker. It smells like a tack room. It also requires more maintenance. If you get the leather version, you’ll need to treat it with a suede protector or a leather conditioner to keep it from drying out and cracking at the flex points. For most casual users, the Birko-Flor mocha is the smarter play. It’s "lifestyle" ready without the "leather care" homework.
How to Tell if Your Size 40 Actually Fits
When you finally get your hands on a Birkenstock Arizona mocha size 40, don't just walk around the carpet and say "yeah, feels fine." You need to check the "foot symbol" on the footbed.
- Filled-in Foot: Narrow fit.
- Outline Foot: Regular/Wide fit.
Most people actually need the regular fit, but many retailers only stock the narrow because it looks "sleeker." For a size 40, if your foot is spilling over the edges of the cork, you’re in a narrow when you should be in a regular. You want about 10mm of space in front of your toes and about 5mm behind your heel. This allows your foot to move naturally as you walk without hitting the rim.
The Longevity Factor: Maintenance is Key
A pair of Arizonas should last you five years. Minimum. If yours are dying after one season, you're doing it wrong. Cork is a natural material. It dries out. If you see the cork on your Birkenstock Arizona mocha size 40 starting to look dull or "fuzzy," you need to apply cork sealer. It’s a $10 fix that saves a $110 shoe.
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Also, stay away from heat. Don't leave them in a hot car. Don't put them by a radiator to dry after a rainstorm. The heat will shrink the EVA sole and can actually cause the cork to crack and pull away from the straps.
Why the Arizona Silhouette Persists
It’s the two straps. Simple. The Arizona provides more lateral stability than the Gizeh (the thong style) or the Madrid (the single strap). Because the straps are adjustable, a Birkenstock Arizona mocha size 40 can accommodate someone with a high instep or someone with very flat feet. You just poke a new hole in the strap if you have to. It's a customizable orthotic disguised as a beach shoe.
Real-World Use Cases
I’ve seen people wear these to weddings in Tulum and to grocery stores in rainy Seattle. The mocha color bridges that gap. It’s dark enough to look "dressed up" with some nice chinos but casual enough for sweatpants. In a size 40, it’s also a very balanced-looking shoe—not so big it looks like a boat, but substantial enough to feel sturdy.
If you’re traveling, these are the ultimate airport shoe. Easy off at security, and they handle the "swollen foot" phenomenon that happens on long flights because you can just loosen the buckles.
Common Misconceptions
People think Birkenstocks are waterproof. They aren't. Unless you buy the EVA version (the plastic ones), keep your mocha Arizonas out of the lake. The cork will absorb water, get heavy, and eventually rot if it stays damp. If they do get soaked, dry them slowly in the shade.
Another myth? That they don't need "breaking in." If you buy the classic footbed Birkenstock Arizona mocha size 40, it will feel like a wooden board for the first few days. That’s normal. Your body weight and heat are literally molding that cork to the shape of your specific foot. Once that happens, no other shoe will feel right.
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Actionable Steps for Your New Pair
First, check the footprint. Before you wear them outside, stand in them on a clean surface. Ensure your heel sits squarely in the cup and your toes aren't touching the edge. If you're a true size 40, your toes should have a "breathing room" gap.
Second, seal the cork immediately. Most new pairs come with a light coating, but adding a fresh layer of cork sealer to the exposed edges will double the lifespan of the footbed.
Third, rotate them. If you wear your Birkenstock Arizona mocha size 40 every single day, the sweat from your feet won't have time to evaporate, which leads to that dark "footprint" stain forming faster. Giving them 24 hours to air out between wears keeps them fresh.
Finally, don't be afraid to take them to a cobbler. One of the best things about Birkenstocks is that they are completely repairable. You can get them resoled for a fraction of the cost of a new pair. When the tread gets thin, spend the $30 to get a new EVA outsole glued on. You’ll keep the footbed you spent months breaking in, but the grip will be like new.
Buy the mocha. Trust the size 40. Just make sure you're getting the width right before you commit.