Roblox CollisionGroups: The Ultimate Guide to Physics Control and Custom Interactions ⚔️

Roblox physics can be chaotic.

Sometimes you want parts to collide realistically, and other times you want them to pass through each other like ghosts.

That’s where CollisionGroups come in — they give you the power to define how different categories of parts interact.

In this guide, we’ll cover what CollisionGroups are, how to set them up, best practices, and advanced use cases that professional developers use to make their games feel polished and intentional.

🤔 What Are CollisionGroups?

CollisionGroups are a feature of the PhysicsService in Roblox. They let you define sets of parts that have specific collision rules.

By default, all parts in Roblox belong to the same group (“Default”), meaning everything collides with everything. But with CollisionGroups, you can tell Roblox:

• “Bullets should not collide with players.”

• “Teammates should pass through each other, but not enemies.”

• “Ghost parts collide with enemies but not with the environment.”

It’s essentially a customizable collision matrix.

⚡ Why Use CollisionGroups?

• Performance – Prevent unnecessary collisions and physics calculations.

• Cleaner Gameplay – Stop players from bumping into their teammates.

• Custom Mechanics – Build features like shields, ghost modes, bullets, force fields, or no-clip systems.

• Consistency – Handle edge cases like accessories colliding with characters.

Without CollisionGroups, you’d rely on hacky workarounds like toggling CanCollide, which isn’t nearly as powerful or flexible.

🛠️ Setting Up CollisionGroups

CollisionGroups are managed by the PhysicsService.

Step 1: Enable PhysicsService

local PhysicsService = game:GetService("PhysicsService")

Step 2: Create Groups

PhysicsService:CreateCollisionGroup("Players")
PhysicsService:CreateCollisionGroup("Bullets")
PhysicsService:CreateCollisionGroup("Props")

Step 3: Define Rules

-- Players should not collide with bullets
PhysicsService:CollisionGroupSetCollidable("Players", "Bullets", false)

-- Players still collide with props
PhysicsService:CollisionGroupSetCollidable("Players", "Props", true)

Step 4: Assign Parts

PhysicsService:SetPartCollisionGroup(part, "Bullets")

Now, that part follows the rules of the group.

📜 Example: Bullet System with CollisionGroups

Let’s say you’re building a shooting game. You don’t want bullets to get stuck on players’ arms or hats.

Now bullets won’t collide with players, but they can still hit the environment.

🎮 Example: Teammates Passing Through Each Other

In a team-based game, it feels clunky if players on the same team bump into each other. You can fix that with CollisionGroups:

PhysicsService:CreateCollisionGroup("RedTeam")
PhysicsService:CreateCollisionGroup("BlueTeam")

-- Same team ignores each other
PhysicsService:CollisionGroupSetCollidable("RedTeam", "RedTeam", false)
PhysicsService:CollisionGroupSetCollidable("BlueTeam", "BlueTeam", false)

-- But they still collide with the other team
PhysicsService:CollisionGroupSetCollidable("RedTeam", "BlueTeam", true)

Now teammates ghost through each other while still colliding with enemies.

🧑‍🤝‍🧑 Handling Characters Automatically

One tricky part: when new accessories, hats, or tools get added, they don’t automatically inherit your CollisionGroup.

That’s why smart devs hook into DescendantAdded on characters:

local function assignGroup(char, groupName)
	for _, part in ipairs(char:GetDescendants()) do
		if part:IsA("BasePart") then
			PhysicsService:SetPartCollisionGroup(part, groupName)
		end
	end
	char.DescendantAdded:Connect(function(d)
		if d:IsA("BasePart") then
			PhysicsService:SetPartCollisionGroup(d, groupName)
		end
	end)
end

This ensures all future parts (like hats or welded tools) follow your collision rules.

⚠️ Common Mistakes & Fixes

1. Forgetting to Assign Groups

   • Creating a group isn’t enough. You must assign each part to that group.

2. Setting Only One Direction

   • Collision rules are bidirectional. If you set A vs. B to false, that covers both directions.

3. Accessory Collisions

   • Remember: hats, hair, and tools are BaseParts too. Always apply CollisionGroups to them.

4. Ragdolls & Extra Parts

   • If you use ragdoll systems, newly created parts also need group assignment.

🔥 Advanced Use Cases

1. Ghost Mode / Spectator Mode

Set a player’s parts into a “Ghost” group that collides with nothing.

PhysicsService:CreateCollisionGroup("Ghosts")
PhysicsService:CollisionGroupSetCollidable("Ghosts", "Players", false)
PhysicsService:CollisionGroupSetCollidable("Ghosts", "Props", false)

Players in ghost mode can fly through the world without affecting it.

2. Shields & Force Fields

You can create a “Shield” group that blocks projectiles but not teammates.

PhysicsService:CreateCollisionGroup("Shields")
PhysicsService:CollisionGroupSetCollidable("Shields", "Bullets", true)
PhysicsService:CollisionGroupSetCollidable("Shields", "Players", false)

3. Performance Optimization

Massive maps with thousands of parts? Put background decorations in a separate group that doesn’t collide with players. This reduces physics calculations.

4. Vehicles & Mounts

Keep players from colliding with their own vehicle by separating them into different groups.

PhysicsService:CreateCollisionGroup("Vehicles")
PhysicsService:CollisionGroupSetCollidable("Players", "Vehicles", false)

📜 Recap & Best Practices

• Use PhysicsService to create and manage CollisionGroups.

• Assign every relevant part to its proper group.

• Use DescendantAdded to handle future parts.

• Disable same-team collisions for smoother gameplay.

• Use ghost groups, shield groups, and vehicle groups for advanced systems.

✅ Final Thoughts | Roblox CollisionGroups

CollisionGroups are one of Roblox’s most underutilized superpowers. They let you fine-tune gameplay so it feels smooth, intentional, and professional.

• Want bullets that don’t break on hats? Use CollisionGroups.

• Want teammates to move cleanly through each other? Use CollisionGroups.

• Want to optimize physics and improve performance? Use CollisionGroups.

Once you master them, you’ll never go back to sloppy CanCollide toggles.

Remember: great physics design isn’t about more collisions, it’s about the right collisions.