The short answer
The replica Ballon Bleu 28mm worth buying is a quartz watch. The genuine Cartier Ballon Bleu in 28mm runs a battery movement, caliber 057, so a 28mm rep with an automatic inside is a mismatch out of the gate. It should measure 28mm across the case, sit around 9mm thick, have no date window, and carry a domed blue cabochon on the crown. If those four things line up, you are looking at a serious example. If any of them are off, walk.
What the genuine 28mm is
Cartier launched the Ballon Bleu in 2007, and the 28mm is the smallest of the family. It reads as a ladies' watch on paper, though plenty of men with slim wrists wear one, since the rounded case sits flat and the lugs curve down tight.
- Case: 28mm wide, polished steel or gold, the signature balloon curve on the flanks
- Movement: quartz, Cartier caliber 057
- Dial: guilloché texture, Roman numerals, blued sword hands, a hidden signature worked into the VII
- Crown: fluted, set with a blue sapphire cabochon and partly shielded by a crown guard
- Strap or bracelet: narrow leather, roughly 14mm at the lugs, or a steel bracelet
- Water resistance: 30m, which means splashes and nothing more
- Complications: none. No date, no seconds subdial
Where replicas give themselves away
The cabochon
Cheap reps glue in a glass bead or a dyed stone with a flat top. The real one is a smooth dome, deep blue, no bubbles, no seam where it meets the crown. On higher tiers the stone is synthetic sapphire and looks right in photos.
Dial texture
The guilloché pattern should catch light and shift as you turn your wrist. Stamped or printed texture looks flat and greasy, and it is the first thing I check in a close-up shot.
Case thickness
A 28mm rep that measures 10mm or 11mm thick will sit like a puck. The genuine is slim, and that slimness is most of the charm.
The second hand
Genuine is quartz, so the second hand steps once per second. If a listing shows a smooth sweeping seconds hand on a 28mm, the seller has either put an automatic in a case that never had one or edited the video.
Movements you will actually find
Japanese quartz from Miyota, Swiss quartz from Ronda or ETA, and a lot of vague "Swiss parts" language. In this size the movement is the least interesting part of the watch, and it is also the cheapest to get right. Do not pay a premium for a movement claim you cannot verify.
Price tiers
- Under $100: usually a glass cabochon, shallow dial texture, rough bracelet finishing
- $150 to $350: the sensible zone, sapphire crystal, decent guilloché, close case dimensions
- $400 and up: diminishing returns on a quartz dress watch this small
What I check before buying
- Case diameter and thickness in millimeters, not adjectives
- A photo of the crown from the side, to see the cabochon shape
- A dial shot in raking light, to judge the texture
- The caseback engraving, including where "Swiss Made" sits
- Whether the seller pressure tests, or admits they do not
Practical notes
Treat any 30m rating as decorative. Do not swim, shower, or do dishes in it, and get the gaskets checked if you plan to wear it daily. Counterfeit watches carry real legal risk in the US, from customs seizure to trademark claims, so buy with your eyes open. Service on a quartz rep is cheap and easy, which is one more reason the 28mm is a low-stress way into this shape.