How to Clear Size Barriers in Roblox Fat vs Skinny Obbies

To bypass physical barriers in Roblox weight-based obstacle courses (obbies), inspect the path ahead to identify space requirements, then touch a size-changing portal or button to toggle your avatar between "Fat" and "Skinny" states.

Selecting the Right Avatar Size for Paths

Progression in size-changing obbies depends on matching your character's collision box to the physical geometry of each platforming segment.

Skinny Model: Use this form when approaching narrow corridors, tightropes, or thin vertical slits. A larger avatar strikes the side walls, triggering collision errors that stop your forward movement or knock you off the platform.
Fat Model: Use this form when encountering wide gaps, heavy pressure plates, or weight-triggered mechanisms. Skinny avatars lack the wider physical footprint or physics weight required to trigger certain interactive platform switches.

If a path appears impassable, look directly around the immediate platform for size-changer portals, buttons, or pads to switch forms before attempting the jump.

Managing Speed, Landing, and Transitions

Switching forms changes how your character handles landing zones and platform edges.

Scan ahead before jumping: Identify whether the landing platform leads into a narrow tunnel or a wide trigger zone before leaving the ground.
Adjust landing precision for larger models: The "Fat" avatar has a broader collision box, making high-precision jumps onto thin beams riskier due to edge clipping. Switch to a "Skinny" model whenever tight landing zones permit it.
Prepare for multi-switch sequences: Transition zones frequently place alternating size pads in rapid succession. Keep your camera angled downward toward the upcoming platform to locate the next size toggle while mid-air.

Troubleshooting Stuck Characters and Collision Glitches

If your avatar fails to move forward despite having the matching size for an opening, the Roblox physics engine may be clipping your character box on adjacent geometry.

Re-align your center of mass: Step back from the opening, center your camera directly behind your character, and walk straight into the corridor without tilting sideways.
Reset the collision box: If an invisible wall prevents movement through a clear opening, step back onto a size-changer pad to toggle your avatar size off and back on. This refreshes the character's collision dimensions with the stage geometry.