Getting your collisions to behave can be a nightmare, so understanding roblox studio meshpart collision fidelity is pretty much essential if you want your players to actually walk through doors instead of getting stuck on invisible walls. We've all been there—you spend hours modeling a beautiful, intricate stone archway in Blender, you import it into Roblox, and then your character can't even walk through the opening. It feels like there's a giant invisible pane of glass blocking the way. That's usually because the collision geometry doesn't match the visual geometry.
In this post, I want to talk about how to actually handle these settings without losing your mind or killing your game's performance. It's a bit of a balancing act, but once you get the hang of it, your maps will feel a lot more polished.
Why Collision Fidelity Even Matters
When you bring a MeshPart into Roblox Studio, the engine has to figure out how other objects (like players or projectiles) should interact with it. If Roblox tried to calculate collisions for every single tiny polygon on a high-detail mesh, the game would crawl to a halt, especially on mobile devices. To prevent this, the engine creates a "collision model," which is a simplified version of your mesh.
The roblox studio meshpart collision fidelity setting is what tells the engine how hard it should try to match that simplification to the original shape. If you leave it on the wrong setting, you'll end up with "phantom hitboxes" where the player bumps into thin air, or "clipping" where things pass through objects they shouldn't.
Breaking Down the Four Main Settings
In the Properties window for any MeshPart, you'll find the CollisionFidelity dropdown. There are four choices here, and each one has a specific job.
Box
This is exactly what it sounds like. No matter how complex your mesh is—even if it's a donut or a spiked ball—the engine treats it like a simple rectangular box. This is the absolute best for performance. If you have a bunch of small pebbles or background debris that players don't need to interact with closely, set them to Box. It saves the physics engine a ton of work. Just don't use it for a doorway, or you'll never get through it.
Hull
Think of Hull like wrapping your mesh in tight plastic wrap. It covers the outer bounds but doesn't "reach" into any holes or concave areas. If you have a solid, lumpy object like a boulder, Hull is usually your best friend. It follows the general shape much better than Box but stays way more efficient than the higher-tier settings. It's the sweet spot for a lot of environmental props.
Default
Roblox tries to be smart here. It uses a decomposition algorithm to create a semi-accurate shape. For a lot of simple things, it works fine. However, it often fails on complex architectural pieces. It's basically the "middle of the road" option that you'll probably find yourself changing the most because it's rarely perfect for specific gameplay needs.
PreciseConvexDecomposition
This is the big one. If you need a player to walk through a hollowed-out tree trunk or stand inside a detailed room, this is the setting you want. It breaks the mesh down into a series of convex shapes to try and match your original model as closely as possible. It's the most "expensive" setting in terms of performance, but for things like buildings or large interactive set pieces, it's usually necessary.
The Secret Weapon: Show Decomposition Geometry
Before you start flipping every single mesh to "Precise," you need to actually see what Roblox is doing behind the scenes. There's a setting in Roblox Studio that most people forget about but it's a total lifesaver. If you go to File > Studio Settings > Physics and toggle on Show Decomposition Geometry, your meshes will turn into colorful, blocky versions of themselves.
These colors show you exactly where the physical hitboxes are. If you see a big purple block covering the entrance to your house, you know your roblox studio meshpart collision fidelity is set too low. This visualization lets you debug collision issues in seconds instead of constantly playtesting and walking into walls to find the "invisible" spots. Just remember to turn it off when you're done, or the neon colors will give you a headache.
Balancing Performance and Gameplay
I see a lot of builders make the mistake of setting every single mesh to PreciseConvexDecomposition because they want "perfect" physics. Please, don't do that. If your game has hundreds of meshes and they're all set to Precise, you're going to see a massive drop in frame rates, especially for players on older phones.
The trick is to ask yourself: "Does the player need to touch this specific part of the mesh?" If it's a roof that players can't reach, set it to Box or Hull. If it's a fence with tiny gaps, maybe use a simpler collision and don't worry about the gaps. You want to save those "Precise" calculations for the things that actually matter, like the floor, doorways, and main paths.
When MeshPart Collisions Just Won't Work
Sometimes, even with the best roblox studio meshpart collision fidelity settings, the engine just can't get a complex shape right. This happens a lot with very thin walls or weirdly shaped interior spaces. If you're struggling with a mesh that keeps giving you wonky hitboxes no matter what you do, it might be time to take manual control.
What I usually do in these cases is set the MeshPart's CanCollide property to false. Then, I build a "hitbox" using regular transparent Parts or basic Wedges. These primitive shapes are incredibly optimized and give you 100% control over where the player can and can't go. It's a little extra work, but for a competitive map where fair collisions are a must, it's often the best way to go.
Dealing with Small Meshes and Large Worlds
Another thing to keep in mind is that Roblox sometimes ignores fine details on very small meshes to save memory. If you have a tiny key or a small tool, the collision fidelity might look like a blob regardless of the setting. On the flip side, if you have a massive mesh that spans an entire city block, the decomposition might get "stretched" and become inaccurate.
If your mesh is huge, consider breaking it into smaller chunks in your 3D modeling software before importing. Smaller, individual MeshParts usually get much better results from the decomposition algorithm than one giant, "everything-in-one" mesh.
Final Thoughts on Tweaking Your Meshes
At the end of the day, managing roblox studio meshpart collision fidelity is about knowing your limits. Use the "Show Decomposition Geometry" tool to see what's actually happening, stick to Box or Hull whenever you can get away with it, and only pull out the Precise setting when it's truly needed for gameplay.
It might feel a bit tedious to go through your assets and click through these settings, but your players will thank you when the game runs smoothly and they aren't getting stuck on every single rock and tree branch. Keep it simple, keep it optimized, and your game will feel a whole lot more professional.