Squash and Stretch Principle. How to add flexibility to your character.

Squash and Stretch is one of the 12 Animation Principles but it’s also a drawing principle used by all character artists, either in 2D or 3D medium. Its best purpose is to create the illusion of weight and elasticity. The absence of its usage will give a feeling of stiff characters and rigid motion.

This article is about the multiple applicabilities of the Squash and Stretch principle from an animated bouncing ball standpoint, to the flexibility of a facial expression or, to the elasticity of the character in motion. There’s the same logic behind all but on multiple layers of details.

What is Squash and Stretch

As the name implies, “squash” and “stretch” means “elasticity” or “flexibility”. It refers to the deformation of a body (mass) in terms of its natural flexibility in connection to the gravity and elastic forces.

Before we go any further, here’s a general framework to keep in mind, the logic that applies from a simple bouncing ball to a character’s full body.

• Squash means compression, is the elastic characteristic that appears during an impact (for example a contact during a falling). It happens on the horizontal axis and has the effect to squeeze or to push the mass together.
• Stretch means extension or tension, is the elastic characteristic that appears before an impact (due to the gravity force) or just after the impact (due to a recoil force). It happens on the vertical axis and has the effect that stretches or pulls the mass.
• Gravity Force (in a free fall for example) is the force that pulls an object down and causes the acceleration of it.
• Elastic Force is the force that returns an object to its original shape after it has been deformed as squashed or stretched (after an impact for example).

Squash and Stretch of a bouncing ball

Any animation book presents the basic logic of motion through the use of simple ball-characters. This is because there’s no need for powerful graphics in order to create the illusion of movement and aliveness. Just a simple circle (2D) or a sphere (3D) will do.

Football, baseball, basketball, billiard ball, golf ball, volleyball, bowling ball, water polo ball, tennis ball, table tennis ball, etc. All these balls can be animated characters. In reality are objects with different characteristics made from either rubber, plastic, or a compound. And if dropped or thrown, they bounce completely differently because of the different level of flexibility and deformation.

The animated bouncing ball is actually a large subject by itself and it needs a dedicated article since it implies the use of all animation principles (and also there’s some physics involved). However, when it comes to the principle of squash and stretch it has the purpose to create the illusion of life through elasticity in time and space (it’s aliveness).

Let’s think of a rubber ball dropped on the ground which bounces until it settles by it self (complete stop). Now, the higher the flexibility of the ball is, this is what happens:

• the ball will stretch down during the fall, due to the gravity force that pulls its weight down.
• the ball will stretch up after each contact with the ground, due to the recoil force.
• the ball will squash with each contact (impact), due to the elastic forces.
• The more elastic the ball is, the higher the 1‘st bounce will be.
• The more elastic the ball is, the more time will take before settling. More bounces are required before a complete stop.

The ball’s elasticity is a visual clue. It tells us what type of ball that is, what material is made of and also, how alive it can be as a character.

Squash and Stretch of a facial expression

Facial squash and stretch means facial elasticity in connection with a facial expression. Psychology says that there are 7 universal emotions, and therefore there are 7 main facial expressions: anger, contempt, disgust, fear, joy, sadness, and surprise.

Anatomically this means that our faces can “provide” the same facial expressions since the facial muscles are working the same for everyone. However, we all have various degrees of flexibility, some much more than others. Think of Jim Carey’s face, how extremely flexible can be.

Any facial expression is created by facial muscles which work all at the same time. It can be symmetric or asymmetric, from low to high flexibility.

When we look at the extremes of facial elasticity, we have:

• Squashed expression: joy (muscles around the eyes are tightened, cheeks are raised, wrinkled around the eyes appear, lip corners raised).
• Stretched expression: surprised (eyebrows raised, mouth open and dropped, eyes large and opened).

So here’s a short reminder of the main facial group muscles. Check out this interactive and simple muscle chart, 3D viewer of facial muscles.

• Muscles around the mouth (oral group).
• Muscles surrounding the nose (nasal group).
• Muscles associated with the eyelids and eyebrows (orbital group).
• Muscles around the ears (auricular muscles).
• Forehead muscles (frontal group).

Squash and Stretch of mouth shapes

This time, squash and stretch principle refer only to the mouth itself, to the mouth shapes created during a speech.

From the animation standpoint, having the right mouth shapes is important for  creating the illusion of speech and for doing so, is necessary to understand the character’s mouth movements in connection to the speech sounds.

Lip-sync animation cannot just be fully explained in a couple of paragraphs, because there are several aspects involved in how humans execute facial movements to produce speech.

Lip-sync is harmony between the lips shapes, tongue position, and jaw movement. In reality is again about the mouth muscles that work altogether.

For now we just look as extreme mouth deformation:

• Squashed mouth: wide and opened mouth (the pronunciation of letter A, E, I).
• Stretched mouth: long and opened mouth: (the pronunciation of letter O).
• Neutral mouth: closed moth (the pronunciation of letter B, M, P).

Squash and Stretch of a body in motion

I’m not referring to the exercises that people are doing in order to relax their body muscles. I’m referring to the character’s body flexibility during a motion sequence.

In order to describe a full body flexibility there’s no need for a complex motion such as an advanced yoga posture or an acrobat motion. A walk, skip, run or jump motion has its own degree of flexibility.

Any motion has its own pattern and characteristics, there are always key possesses that we consider them to be the “squashed” and “stretched”.

With this in mind here is a look at some simple but effective examples.

• Squashed position (compressed posture), it happens when the entire body’s weight drops down or is being pulled down, due to the gravity force.
• Stretch position (extended posture), it happens when there’s enough momentum to go in and out of a squashed pose.

Takeaway

So there you go, Squash and Stretch 101. The key aspects to remember are:

• Squash and Stretch are deformations of a mass that implies “elasticity” and “flexibility”.
• The absence of its usability will create a feeling of stiff characters and rigid motion.
• Squash and Stretch are two key postures that cannot exist one without the other, are opposite forces that complete each other.
• Every Squash and Stretch must have a clear Line of Action (check out my article on Line of Action Principle)
• Every motion sequence has a Squash and Stretch key postures.
• It gets more accentuated in dynamic mechanics such as sports.
• It gets exaggerated in a cartoon style but in a way that the mechanics still look believable.

I always say the same thing. When you draw or animate a character, analyze the character’s posture and motion as in a real-life situation. If you want to create a believable character you must understand the physical mechanics.

Be a “scientist of art” by exploring multiple layers of the craft. Always remember that art comes from real life, it’s only an interpretation of what we see.

Take time every day to explore the things around you, how they look, and how they move, and allow yourself to become aware of the repetitive patterns that you see. This awareness is the start of making art that makes sense.

Related articles

Check out other animation and drawing principles.

• Principle of Line of Action, the key for adding attitude in the character’s posture or, dynamism in its movement.
• Stickman drawing for animators, how to sketch a complex motion by using a simplified way of visualization.