View 3MF files from your slicer online — no install needed

A 3MF file is the 3D Manufacturing Format — the native project format that Bambu Studio, PrusaSlicer, Cura, and OrcaSlicer write when you save your work. Unlike an STL, which is just a bag of triangles, a 3MF bundles colour, multi-part assemblies, and printer settings into one container. Loft’s 3MF Viewer opens one in a browser tab: orbit, measure, screenshot, no upload and no slicer install.

What a 3MF file actually is

3MF stands for 3D Manufacturing Format. It’s a zipped container — XML geometry plus optional metadata — designed by the 3MF Consortium to replace STL as the file you hand to a 3D printer. The format fixes STL’s biggest gaps: it can store the model’s colour, group several parts into one assembly, and embed slicer-specific settings like supports and print profiles.

In practice, 3MF is the project file your slicer saves. When you open a design in Bambu Studio or PrusaSlicer, arrange a few parts on the plate, and hit save, you get a .3mf. That single file is the thing you reopen later, or send to a friend, or attach to a print-farm order.

Who needs to open one — and the usual pain

The people who hit a .3mf they can’t open are usually not the person who made it. You download a model from a sharing site, a client emails you their slicer project, or a teammate drops one in a shared folder. Now you want to look at it before committing to a 90-minute print.

The standard answer is “install the slicer.” But the slicer that wrote the file might not be the one you have. Bambu Studio, PrusaSlicer, Cura, and OrcaSlicer are all separate multi-hundred-megabyte desktop apps, and a 3MF from one doesn’t always feel at home in another. The other option — a web viewer that uploads your file to a server — is the one I’d think twice about when the model is a paid design or a client’s product.

How Loft opens it

Loft’s 3MF Viewer renders the geometry in a Three.js WebGL2 orbit scene, using three.js’s built-in ThreeMFLoader to parse the container. Drag the file in or use the file picker — the format is auto-detected, so you don’t pick a “3MF mode” first. Left-drag orbits, right-drag (or two-finger trackpad drag) pans, scroll zooms, and a reset-camera button frames the whole model in one click.

Multi-part 3MFs load as a single unified scene. A 3MF can hold many meshes — the body, the lid, the screws — and all of them appear together the way the slicer arranged them, with colour assignments preserved where the loader supports them. You can flip between shaded and wireframe to inspect how individual parts sit relative to each other.

Measure and screenshot

Two things turn “I can see it spin” into “I can actually use this.” First, point-to-point measurement: click Measure, then click two surface points, and the distance shows in the file’s native units — typically millimetres. On a multi-part model the picker walks every mesh in the scene, so you can measure across parts, not just within one. Second, PNG export: the screenshot button captures the current camera angle as an image, which is the quickest way to show someone “this is the model” without sending the file at all.

The viewer also drops the triangle count and file size into the status footer, so you get a rough sense of how heavy a model is before you send it off to slice.

The part that matters: nothing uploads

Here is the whole point. Parsing and rendering happen entirely inside your browser tab. The .3mf bytes are read straight into WebGL — there is no server round-trip, no upload, no copy sitting in someone’s cloud bucket. This is the moat for Loft’s local-first architecture: a proprietary design or a client’s product file never leaves the device, which means you can open it on a shared machine, a borrowed laptop, or airplane wifi without thinking about who else can see it.

Because the work is local, the viewer also keeps working offline after your first visit — it’s a PWA, so the tab caches itself. Open a .3mf on a plane; it just renders.

Honest limits

I’ll be straight about two things. The viewer is read-only — it shows you the model and measures it, but it won’t let you edit, re-slice, or change print settings. For that you still need the slicer. If you want to modify the design, this isn’t the tool; if you want to inspect it, it is.

The second limit is the loader. The underlying ThreeMFLoader has known edge cases with some 3MF variants — a few project files, especially ones packed with embedded slicer settings, don’t fully parse. If a file refuses to open, the reliable fix is to re-export from your slicer as a plain 3MF (geometry, not a full project archive), or fall back to STL and drop that instead. Loft’s viewer happily takes STL, OBJ, PLY, GLB, and glTF on the same drop target, all auto-detected.

It runs the same everywhere

Because the whole thing is a Three.js scene running on WebGL2, there’s nothing OS-specific about it. The same tab works on Windows, macOS, Linux, ChromeOS, and reasonably modern phones and tablets — no “Mac version coming soon,” no architecture builds. The 3MF Viewer is one thin landing page over Loft’s shared mesh viewer; the STL, OBJ, PLY, and GLB pages are the same engine pointed at a different default format. If your day involves more than one of those, the muscle memory carries over.

If you want the fuller story of how a 3D CAD viewer ends up running in a phone browser without uploading anything, the Gerber viewer case study walks through the engineering, and the 3D-file overview covers the shared mesh path across formats.

Takeaway

If you’ve got a .3mf from a slicer and you just need to see it — check the parts, measure a clearance, grab a preview image — you don’t need to install Bambu Studio or trust an uploader. Drop it into the 3MF Viewer and it renders in the tab. Read-only, no upload, gone when you close the tab. That’s the entire pitch, and most days it’s exactly enough.