Blender Cloth Simulation: Internal Air Pressure and Cloth Springs Tutorial

Remember when cloth simulation in Blender felt like trying to tame a particularly moody sheet ghost? Everything just... drooped. Sure, it was technically cloth, but getting anything that held volume or bounced back like an actual object was a nightmare. Well, the ghosts have been exorcised. Blender 2.8 brought us Internal Air Pressure and Cloth Springs, and honestly, these two features are some of the most fun you can have with physics since, well, since the fluid sim got its glow-up.

This tutorial from Blender Mania 3D (featuring Alec Scoreboard’s signature enthusiasm) walks through both systems with a level of clarity that makes you wonder why you ever found cloth sim intimidating. Let’s break down what these features actually do - and why you’ll probably spend your next three weekends experimenting with bouncing balloons and squishy cubes.

Internal Air Pressure: Giving Cloth Actual Volume

The Internal Air Pressure feature solves a problem that’s plagued cloth artists forever: cloth without volume is just a surface. Even when you wanted something inflated - a beach ball, a balloon, a beanbag chair - you had to fake it with shape keys or external forces. It worked, but it never felt right.

Enter Internal Air Pressure. Now your cloth meshes can behave like they contain actual air. Positive pressure values inflate your mesh like a balloon filling with helium. Negative pressure deflates it, like something getting vacuum-sealed. The result is cloth that responds to internal forces rather than just gravity and collisions.

The magic happens in the Cloth Physics modifier under the Pressure section. You’ve got several sliders to play with:

• Pressure: The core value - positive inflates, negative deflates, zero means flat cloth physics as usual
• Factor: A multiplier that scales the pressure intensity. Crank this up and even small pressure values create dramatic effects
• Custom Volume: Sets the initial “fullness” of your mesh. Zero does basically nothing - set it to 1 or higher to actually see results
• Target Volume: Controls how aggressively the simulation tries to maintain a specific volume

Want a beach ball that bounces? Positive pressure. Want a balloon that sags when it hits the ground then reinflates? Animate the pressure from negative to positive with keyframes. The tutorial demonstrates all of this with live playback - including the delightful moment where a beach ball deflates on impact, squishes realistically, then pops back to full inflation.

Animating Pressure for Narrative Effects

Here’s where things get genuinely cool. By keyframing the Pressure and Factor values, you can create narrative physics - cloth simulation that tells a story.

Alec demonstrates this with three distinct effects:

1. The Bounce-and-Reinflate: A ball hits the floor, pressure drops negative (deflation), then springs back to positive. It squishes instead of just colliding.
2. The Pop: Mid-simulation, pressure spikes to a sharp negative value. The balloon implodes. Dramatic, effective, and honestly pretty satisfying to watch.
3. The Floating Escape: Using vertex groups to apply pressure only to specific vertices, a deflated balloon suddenly rises and drifts away. This one’s pure magic - the bottom sags, the top gets positive pressure, and the whole thing floats upward like a proper helium balloon.

That last one is worth emphasizing because it’s genuinely clever. Vertex groups in cloth simulation let you localize pressure to specific parts of your mesh. Assign a vertex group to the top hemisphere of your sphere, enable pressure for just that group, and suddenly you have directional inflation that creates lift. It’s the kind of technique that opens up all kinds of possibilities - directional wind effects on capes, localized breathing on characters, balloons that deflate from the bottom first.

Cloth Springs: When Soft Body Meets Cloth

If Internal Air Pressure gives cloth volume, Internal Springs give it structure. This feature essentially turns your cloth mesh into a soft body simulation with internal resistance - springs that exist inside the mesh, not just along its surface.

Why would you want this? Because real cloth isn’t infinitely deformable. A beanbag compresses, but it doesn’t collapse into a pancake. A filled cushion has internal resistance. Even something like a water balloon has structural integrity - it jiggles, sure, but it doesn’t just fold in on itself.

The tutorial demonstrates this with a subdivided cube (Alec uses Blender’s subdivide tool to add enough geometry for the springs to actually work). With Internal Springs enabled, the cube behaves less like a bedsheet and more like a... well, like a springy thing. It bounces. It compresses under force then rebounds. It holds its shape better while still being clearly soft.

The key settings here:

• Max Spring Creation Length: Controls which vertices get connected by internal springs. Set to 0 and it’s infinite - every vertex connects to every other vertex. Set it to 2 or 3 and only nearby vertices connect, creating a very different bounce behavior
• Check/Max Creation (diversion): An angle-based filter that prevents springs from forming when they’d deviate too far from vertex normals. Default is 45 degrees - adjust this to control spring density
• Tension Stiffness: How much the mesh resists stretching. Higher values approach rigid body behavior
• Compression Stiffness: How much the mesh resists squashing. Crank this and your object barely compresses at all

The interaction between tension and compression stiffness is particularly interesting. High tension makes your object resist stretching - think of a tightly inflated balloon that barely deforms. High compression makes it resist squashing - more like a foam cushion that pushes back. Combine both and you get something that feels almost solid while still having that subtle cloth/soft body wobble.

Connecting to the Broader Blender Ecosystem

These features don’t exist in isolation - they plug directly into Blender’s existing cloth and collision systems. Your cloth still responds to wind forces. It still collides with objects (Alec uses a simple plane as a collision floor). It still respects the quality steps, bend resistance, and other cloth settings you’ve already learned.

What Internal Pressure and Springs give you is range. You can now make cloth sim work for objects that were previously the domain of rigid or soft body physics. Inflatable structures, cushions, stuffed animals, balloons, beanbags - things that need volume and internal resistance but still behave like cloth on the surface.

For character work, this opens up possibilities for clothing that actually fits over body parts with volume, rather than just draping. For environment work, it means props that deform realistically under impact. For abstract motion graphics, it means bouncy, organic forms that feel alive without the computational cost of full soft body simulation.

The tutorial wraps with Alec’s characteristic enthusiasm: “Go crazy, experiment, have fun.” It’s good advice. These tools reward exploration. Every combination of pressure values, spring lengths, and stiffness settings produces something slightly different. Some combinations will be exactly what you need. Others will be happy accidents that spark new ideas.

Recommended Gear for This Tutorial

Wacom Intuos Small Graphics Drawing Tablet View on Amazon

ENDGAME GEAR OP1 8k v2 Gaming Mouse View on Amazon

Watch the Tutorial

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Blender for Beginners Part 1: Reference Guide View on Amazon

VEIKK Studio 16 Drawing Tablet with Screen View on Amazon

The Bottom Line

Internal Air Pressure and Cloth Springs are the kind of features that fundamentally expand what cloth simulation can do in Blender. They’re not incremental improvements - they’re new categories of behavior.

Start with Internal Pressure if you want volume. Play with negative values for deflation effects, positive for inflation, and keyframes for animated transitions. Use the Factor slider to control intensity without changing your base pressure value.

Add Internal Springs when you need structure. Adjust the creation length to control which vertices connect, and dial in tension/compression stiffness until you hit the sweet spot between cloth drape and solid bounce.

And seriously - try the vertex group trick with localized pressure. There’s something deeply satisfying about making one end of an object float while the other stays grounded. It’s the kind of technique that feels like cheating, except it’s exactly what the feature was designed for.

Happy simulating. Go make something bouncy. 🙂