Rubber hose animation in Blender: bendy limbs with no elbows

Noodle arms that swing like tubes, white gloves, solid black eyes with a wedge cut out, and everything bouncing to the beat: that is the rubber hose style of early 1930s cartoons. This guide covers what defines it, then how to build a rubber hose limb in Blender, in 3D and in 2D.

What is rubber hose animation?

Rubber hose was the first animation style to become standardised in the American animation industry. Its signature is the limb: arms, and sometimes legs, drawn as flowing curves with no hinged elbows or knees. Hence the name: in motion, the limb curves like a rubber hose.

The style took shape in the 1920s in New York, where American cartoon studios were based at the time. Animator Bill Nolan is credited with introducing it on Felix the Cat: he gave Felix a rounder design that was quicker to draw, with rubbery limbs that could stretch a long way or be tied in knots. Mickey Mouse, from Steamboat Willie in 1928, and Betty Boop are the best-known examples.

It fell out of fashion in the late 1930s as studios moved towards realistic anatomy, a shift in which the success of Snow White and the Seven Dwarfs (1937) played a key part. Interest has returned since the early 2010s, notably with the video game Cuphead and Disney's 2013 short Get a Horse!, which combines black-and-white hand-drawn animation with colour CGI.

What defines the style

• Limbs without joints: from shoulder to hand, the arm is one curve that can lengthen, shorten and bend anywhere.
• Simple shapes: Mickey's body, for instance, was built from circles to make him easy to animate.
• White gloves: on a black body, a black hand vanishes when it passes in front of the torso. A white glove keeps it readable. Mickey wears them from 1929 onwards.
• Pie eyes: solid black eyes with a white slice taken out, like a pie with a piece missing.
• Bounce and stretch: characters and objects bounce around, often in time with the music. Squash and stretch is deliberately visible.

The principle in Blender: a bone that bends

A regular bone is rigid: an arm made of two bones bends at a single point, like a real elbow. Bendy Bones (B-Bones) are designed to replace long chains of small rigid bones. Blender treats each bone as a section of a Bézier curve and splits it into segments that follow it, which is exactly the jointless limb of rubber hose.

You only see the curve when the armature is shown as B-Bones: Armature properties, Viewport Display panel, set Display As to B-Bone. The Blender rigging guide covers armature and weight basics.

Step 1: a Bendy Bone arm

1. Add an armature (Add > Armature), switch to Edit Mode and place the bone from shoulder to wrist. If you plan to use an IK chain (step 3), extrude a second bone from its tip with E: it is created as a connected child of the first.
2. In the Bone tab, Bendy Bones panel, raise Segments. Higher values give a smoother bend but a heavier pose calculation, so stop once the curve looks smooth.
3. Select the mesh, then the armature, and press Ctrl+P > Armature Deform > With Automatic Weights. The arm needs enough edge loops along its length to bend.

The same panel shapes the curve:

• Curve In/Out offsets the curve handles perpendicular to the bone, so it arcs while its ends stay put.
• Ease In/Out lengthens or shortens the handles at each end, which sets how round the curve is near the shoulder or the wrist.
• Scale In/Out sets the thickness at each end, for an arm that tapers from shoulder to wrist.

Each of these properties exists twice: in Edit Mode they define the rest shape, and in Pose Mode they combine with it and can be animated. If the rest pose is strongly curved, set Vertex Mapping to Curved: deformation improves, at the cost of speed.

Step 2: driving the curve with control bones

Rather than keying Curve In/Out pose after pose, hand the curve over to two control bones, one at the shoulder and one at the hand. They should not deform the mesh, so turn off Deform in the Deform panel of their bone properties. Under Custom Handles, pick a type for Start Handle and End Handle, then the bone to use: the shoulder at the start, the hand at the end.

• With Tangent, the handle follows the control bone's orientation, regardless of its location, so rotating the hand bends the whole arm.
• With Absolute, it follows the control bone's position, which must stay a nonzero distance from the arm.
• The Custom Handles Scale and Ease checkboxes multiply thickness and easing by the control bone's scale, so scaling up the hand bone thickens the wrist.

Step 3: arms that stretch

With the Stretch To constraint

In Pose Mode, give the arm bone a Stretch To constraint targeting the hand bone. The bone points at its target and scales towards it, along its local Y axis. Original Length is the distance at which there is no stretch. With Maintain Volume on XZ, the arm gets thinner as it stretches and thicker as it shortens, which the manual describes as useful for squash and stretch on stylised characters; on None, the thickness stays the same.

The hand bone must not be a child of the arm: a child inherits its parent's location, rotation and scale, so it would follow the very bone it is meant to pull. Check the Parent field in the Relations panel.

With an IK chain

For an arm that bends in a chosen direction, keep two connected bones, both set up as Bendy Bones: in a connected chain, the segments blend smoothly into each other and the elbow becomes a curve. On the forearm, add an Inverse Kinematics constraint (Shift+I), target the hand bone, set Chain Length to 2 and add a Pole Target to aim the bend. To let the chain lengthen, enable Stretch on the constraint and give each bone an IK Stretch value above 0 (Bone tab, Inverse Kinematics panel). Without it, the option does nothing.

Step 4: holds, timing and bounce

In Pose Mode, I keys the channels set in your preferences. To include the B-Bone shape, press K and pick the BBone Shape keying set, which covers every Bendy Bones property.

• Holds: two identical keys a few frames apart hold the pose. Auto Clamped handles (Key > Handle Type, V) stop the curve from overshooting between them.
• Choppy timing: the Stepped Interpolation F-Curve modifier holds each value for Step Size frames.
• Bounce: in the Graph Editor, Key > Interpolation Mode (T) offers Bounce, which makes the value bounce as it settles, and Back, which with Ease Out overshoots the target and comes back.
• Loops: Channel > Extrapolation Mode (Shift+E) > Make Cyclic repeats the curve. The walk cycle in Blender guide walks through the method.

For a very fast gesture, an arm stretched over a single frame works as a smear: see the guide on smear frames in Blender.

The 2D route with Grease Pencil

To stay in drawing, use Grease Pencil. The File > New > 2D Animation template sets a front-facing drawing plane, prepares Line and Fill layers and creates a keyframe whenever you draw on an empty frame.

• In Draw Mode, draw each arm as one curved stroke, with no corner at the elbow.
• Onion Skinning shows ghosts of the keyframes before and after the current frame.
• Interpolate (Ctrl+E) adds in-betweens between two simple drawings; Interpolate Sequence (Shift+Ctrl+E) fills every frame between them.

For a drawn character animated with a skeleton, the Grease Pencil Armature modifier deforms the strokes: bound to Vertex Groups, a bone only moves the points in the group that shares its name. The Grease Pencil in Blender guide introduces the tool.

Rendering the look: cel shading and flat colour

For a flat-colour look in EEVEE, a Diffuse BSDF fed into a Shader to RGB node and then a Color Ramp gives a flexible toon shader; that node does not exist in Cycles, which offers the Toon BSDF instead. The Grease Pencil Line Art modifier draws outlines as seen from the active camera. The cel shading in Blender guide has the details, colour management included.

Common mistakes

• The arm bends at an angle: Segments is set to 1, or the mesh lacks edge loops. If only the bone looks straight, the armature is not displayed as B-Bones.
• The hand follows the arm instead of pulling it: the control bone is still a child of the bone it drives.
• The IK chain will not stretch: Stretch is enabled but IK Stretch is still 0 on the bones.
• The curve gets lost between keys: the Bendy Bones properties were not keyed. Use the BBone Shape keying set.

Rendering a rubber hose animation

Rubbery motion can only be judged at full speed, with final lighting and materials. Render a few dozen frames first, before starting the full sequence. For engine and graphics card settings, see the guide on how to render in Blender.