STL, 3MF, OBJ or STEP: Which File Do You Send to a 3D Printing Studio?

You have a 3D model, or a link to one, and want it printed. Then the studio asks "can you send the STL?" and you are not sure what that means or whether the file you have is right. This guide explains the four formats you will meet, which one a studio prefers, and how to get it out of whatever program you are using.

What a 3D print file actually is

A 3D printer does not read pictures or drawings. It needs a description of a closed 3D shape, which the studio's software then slices into thin horizontal layers and turns into machine movements. Every format below is just a different way of storing that shape, with more or less extra information attached.

The key thing to understand: the studio needs the geometry, not a rendering, a screenshot or a PDF. A beautiful image of a model cannot be printed until someone rebuilds it in 3D.

The four formats, compared

Format	What it stores	Best for	Watch out for
STL	Surface as a mesh of triangles	Almost everything; the universal default	No units, no colour, no scale information
3MF	Mesh plus units, colours, multiple objects, print settings	Multi-part and multi-colour prints, modern slicers	Less common in older software
OBJ	Mesh plus texture and material references	Models from sculpting or game tools	Textures are ignored by printers; can be huge
STEP	Exact mathematical solids (CAD)	Engineering parts, anything that needs editing	Must be converted to a mesh before printing

STL: the safe choice

STL is the oldest and most widely supported format. Every slicer opens it, every marketplace sells it. Its weakness is that it stores only triangles, with no record of what units they are in. A file exported at "100" might mean 100 mm or 100 inches. Always tell the studio the size you want in millimetres, and the ambiguity disappears.

3MF: the modern choice

3MF is what STL should have been. It records units, can hold several objects in one file, keeps colour and material assignments, and can even carry print settings. If your software offers 3MF export, use it. For a multi-colour print or an assembly of several parts, it saves the studio a lot of guesswork.

OBJ: fine, with caveats

OBJ files come from sculpting programs like Blender or ZBrush and from game asset sites. They print just as well as STL, but the texture files they reference (colours painted onto the surface) do nothing on a printer. If your model's colour lives in a texture, ask about painting after printing instead.

STEP: for engineering parts

STEP files come from CAD programs like Fusion 360, SolidWorks or FreeCAD. They describe exact curves and dimensions rather than triangles, which makes them ideal when a part must be adjusted: a hole enlarged, a wall thickened, a tolerance changed. A studio will convert STEP to a mesh for printing, and can do it at any resolution, so curved surfaces come out smooth.

What to send, in order of preference

1. 3MF, if you have it, with the size confirmed.
2. STL with the intended size written in the message.
3. STEP for functional or mechanical parts, especially if fit matters.
4. OBJ if that is what you have. It works.
5. A link to a model on a marketplace, and the studio will download the right file. Licences matter here; see licences and commercial use.
6. Photos, sketches or a description if you have no file. Fantasy Lab 3D offers custom modelling, and this article on starting without a model explains how it works.

Formats not to send: PDF, PNG, JPG, DWG or SKP drawings, PowerPoint. These can be a starting point for modelling, but they are not printable.

How to export from common programs

• Blender: File, Export, STL or 3MF. Tick "Selection Only" if the scene has other objects. Apply scale first so 1 unit equals 1 mm or 1 m consistently.
• Fusion 360: right-click the body, Save as Mesh, choose STL or 3MF, refinement High. For STEP use File, Export.
• Tinkercad: Export, then choose STL or OBJ. Tinkercad works in millimetres, which is convenient.
• SketchUp: File, Export, 3D Model, STL. Make sure the model is a solid group with no missing faces.
• Marketplaces (Printables, Thingiverse, Cults, MyMiniFactory): download the model files, not the images, and send the ZIP as is.

What the studio checks after receiving your file

A good studio does not just hit print. Before quoting, Fantasy Lab 3D opens the file and checks that the mesh is watertight (no holes or inverted faces), confirms the scale with you, decides on orientation, looks for thin walls that will not survive printing, and plans supports. Small problems can usually be repaired on our side. Bigger ones, such as a model made of intersecting shells or walls thinner than a nozzle, need a redesign, and we will tell you before you commit. The rules that make a model print well are collected in designing for 3D printing.

Ready to order?

Send your STL, 3MF, OBJ or STEP to Fantasy Lab 3D through the contact section, or DM us on Instagram @fantasylab3d.almaty. If you only have a link, a photo or an idea, send that instead, and we will tell you what the next step is.