First of all, these kinds of terminologies are for the edge processing of the mobile phone protective film.
1) 2D refers to the traditional tempered glass screen protector without edge polishing treatment, we see it as 2D flat screen guardian, after this kind of protector is installed, when you hold your cell phone it feels stuck in the hand which is not good experience, and the edges are easy to be damaged by impact. Now it has been gradually eliminated by the market.
2) 2.5D edge tempered glass screen protector finishing the edge is deal with CNC polishing, so that the edge has a certain arc, handling feelings is relatively smooth, of course, the process is compared complex, the cost is much higher than the flat edge , is the current mobile phone screen protective film used in the production process.
3) 3D screen protective film is mainly designed and produced for curved surface mobile phone such as the first curved edge screen Samsung S6 Edge. The production process is from one piece of glass though hot bending on the shapes of the moulds. then we will have different models for kinds of screens. In addition there are some 2.5D edge mobile phones we make screen protector full screen covered, we also call it 3D curved edge, however it shows product fully attached attribute, for instance Mietubl 11D Full Curved which shows the 3D curve of the phone's screen.
4) 4D, 5D, 6D, 9D, 11D, etc., there is no product difference, mainly due to the market of each product distinction and self-derived name code, cannot define the product characteristics.
5) For the explanation of the above three points, the customer can refer to the following pictures for a more intuitive understandings.