# Help On Collision Fidelity

Hello,

I have just noticed a property that only shows up on union operations and meshparts. Collision Fidelity. I have read other posts like this one: Solid Model Collision Fidelity options enabled but I still don’t understand.

Here are my questions on it:

What even is collision fidelity and what effect does it have on the object?

Why does the collision fidelity property only show up on mesh parts and union operations and not Instance.Part?

What is box property?

What is default property?

What is hull property?

What is preciseconvexdecomposition property?

Thanks if you can get to me, have a wonderful day
BIaughing

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What even is collision fidelity and what effect does it have on the object?

Collision fidelity allows you to control how Roblox calculates the physics of your models to better balance function and performance.

Why does the collision fidelity property only show up on mesh parts and union operations and not Instance.Part?

Since parts aren’t dealing with complex geometry, the property only applies to meshparts and unions.

What is box property?

Box fills in the bounds of the object and treats its collision as such:

What is default property?

Default is a rough calculation of the object’s collisions:

What is hull property?

Hull fills in all convex parts of the object and calculates collision accordingly, as if covering the model in shrink wrap:

What is preciseconvexdecomposition property?

Precise convex decomposition prioritizes surface geometry to produce the most accurate collision of the three—it’s mostly helpful for making sure objects and characters can fit inside certain things that Default or Hull don’t allow (at the expense of performance):

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Thanks for the reply, just wondering what a convex part is

Edit: And what is a shrink wrap?

Edit: What is shrink wrap?

Say you had Saran Wrap. And you wanted to cover an object with a hole with it. You’d have to wrap the entire object around, and as we all know, you can’t not cover something with a hole with shrink wrap. So basically, it’d be the proper shape, but all holes in the part would still have collision even where holes are.

Little side note: If you can, please leave a if this helped. I need to know how to improve my comments.

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So your talking about a shape that is kinda like a donut?

So your talking about a shape that is kinda like a donut?

Yes! That “donut” shape would still have collision around the hole, like it was wrapped with Saran Wrap! I hope that’s easy to understand.

Little side note: If you can, please leave a if this helped. I need to know how to improve my comments.

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Excuse my ignorance, but what is a ‘saran wrap’?

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It’s basically thin, see-through, plastic aluminum foil. You use it to wrap food (most of the time) to keep it in place, or in order to keep it fresh. I don’t use it much, but that’s pretty much what it is.

Little side note: If you can, please leave a if this helped. I need to know how to improve my comments.

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So a shrink wrap is basically like a skin or texture that you would wrap around a 3D object? Edit: And if you had holes in the model, the holes would be covered up by the wrap?

I know this is an old thread and all. But can you actually help me decide on which is the best collision fidelity for my custom mesh character rig? I was using the preciseconvexdecomposition but got into box for a bit.
Could u suggest me a good one?
TY

For some reason I don’t even see the option to set collisionfedelity to box anymore

You’re a lifesaver, btw. This entire time I’ve been making unions with separate collision parts.

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