The Galaxy Z Flip 4 (SM-F721) folds to 84.9 x 71.9 x 15.9–17.1 mm and opens to 165.2 x 71.9 x 6.9 mm. It weighs 187 g, has a 6.7-inch foldable main display and a 1.9-inch cover display, a 3,700 mAh battery and 25 W charging. It is rated IPX8 — water resistant, with no dust rating at all.
That last detail drives everything. Grit is the enemy of a foldable, and a case's most important job on this phone is not absorbing impacts. It is not interfering with the fold.
The rules that apply to every Z Flip case
- It must let the phone close completely flat. If there is a visible wedge at the top when shut, the case is wrong. A gap lets grit into the fold, and grit in the fold is the failure that ends these phones.
- It must clear the 1.9-inch cover display and the two rear cameras, which sit in the same strip.
- It must not add thickness at the hinge. The Flip 4's hinge is narrower than the Flip 3's, which is why Flip 3 cases do not transfer.
- Never put tempered glass on the inner screen. It is a plastic-topped flexible panel with a factory-applied protective layer. Glass cannot fold.
Best overall: hinge protection case
Most two-piece flip cases leave the hinge entirely exposed, which is the phone's most vulnerable component. A design that wraps that section covers the gap.
Check the hinge cover does not bind when opening. It should add resistance you can feel but not resistance you have to fight.
Best for grip: ring stand with camera protection
A folded Flip is a small, thick, slippery block, and an open one is a long, thin lever. Both are easy to drop. A ring gives you a finger anchor in either state and props the phone for hands-free video.
A ring also gives you a magnetic car mount anchor, which the phone itself does not provide — there are no magnets in a Z Flip 4.
Best for carrying cards: wallet case
A Flip folded is already close to wallet-sized, so adding card storage is a natural fit for this phone in a way it is not for a slab.
Watch the thickness: a card pocket on the outer half adds to an already 17 mm folded stack, and it must not prevent the phone closing flat.
Best for hands-free carry: strap and bracelet cases
Wrist and bracelet straps suit flip phones particularly well, because the folded form is small enough to dangle without swinging awkwardly.
Check the strap anchor is moulded into the case rather than glued on — a strap that detaches under load is worse than no strap.
Best slim option: drop protection bumper
If you want minimal added bulk, a bumper covers the corners and edges without wrapping the whole phone.
Browse the full range in the Galaxy Z Flip 4 Cases collection.
Screen protection: what is and is not safe
You can and should protect the 1.9-inch cover display — it is conventional Gorilla Glass Victus Plus and takes tempered glass normally. You can and should protect the rear camera lenses, which are exposed whenever the phone is closed in a pocket.
The inner display is different. Samsung fits a protective layer at the factory. Leave it alone. If it starts peeling at the edges, that is normal wear and a Samsung service centre can replace it — peeling it off yourself and running the panel bare is how these screens get scratched. If you do need to cover it, use only flexible film sold specifically for foldables.
Frequently asked questions
Will a Z Flip 3 case fit a Z Flip 4? No. The Flip 4 is 1.5 mm shorter folded with a narrower hinge, so a Flip 3 case leaves a gap at the fold line.
Will a Z Flip 5 case fit? No. The Flip 5 has a 3.4-inch cover display against the Flip 4's 1.9-inch, so the cutout is completely different.
Is the Z Flip 4 dust resistant? No. IPX8 covers water only. There is no dust rating, which is why keeping the phone closing flat matters so much.
Does the crease get worse over time? The crease is inherent to the design and generally stable. What degrades a foldable is grit and moisture in the hinge, not the fold itself.
Can I use a magnetic mount? Only via a case with a metal plate or ring built in. Avoid mounts that clamp across the hinge.
How do I confirm my model? SM-F721 is the Z Flip 4. Check Settings > About phone, or ask via the Contact page or 978-797-0223.
The bottom line
On a Z Flip 4 the case's first job is letting the phone close completely flat. After that, cover the hinge, protect the cover display and lenses, and add a ring or strap so you stop dropping it. Never put glass on the inner screen.