If you handed me a blob of putty and told me it could “feel” stretching, I would have laughed a few years ago. Putty is for bouncing, pulling, and making terrible sculptures. Sensors are for lab benches and circuit boards. And yet, g-putty is both.

In our work, we mix a tiny amount of conductive graphene (the “g”) into a soft, silly, stubbornly squishy material. The result is a putty that changes its electrical signal when you stretch it, press it, or twist it. It’s like the material has a built-in way of translating motion into data! But it's not because g-putty is magic; it's because it holds a secret map inside.

A city made of carbon

The easiest way I’ve found to picture g-putty is as a city at night. Graphene flakes are like streetlights scattered through a dark landscape. Electricity can travel, but only if enough of the lights are close enough together to make a connected route. When the graphene flakes are too far apart, there’s no continuous pathway for electricity to travel and the putty behaves like an insulator (Fig. 1). But once you add just enough graphene, something dramatic happens: the “city” suddenly connects. Current can find a route across the material (Fig. 2). That sudden change is called a tipping point (scientists often call it a percolation threshold). I like it because it feels like one of those movie moments where the whole map lights up at once.

Stretching breaks the shortcuts

Now comes the part that turns a blob into a sensor. When you stretch g-putty, you don’t just change its shape. You change how graphene flakes sit relative to each other (Fig. 3). Some flakes pull apart. Some contacts weaken. Some “shortcuts” disappear. That means the putty’s ability to conduct electricity changes as it moves. Stretching often makes it harder for current to pass through the putty (resistance increases). Letting it relax often makes it easier again (resistance decreases). Essentially, g-putty is a material that can report its own deformation.

The weirdly satisfying part: the “sweet spot”

One of the most satisfying parts of this research is tuning the material to find its sweet spot. If you add too little graphene, the network isn’t connected and the signal is weak or unstable. If you add too much graphene, everything becomes connected all the time and stretching doesn’t change much. The sensor becomes boring (Fig. 4). But right near that tipping point, g-putty can become incredibly sensitive, because small motions cause big changes in the network. Essentially, the best sensors live right on the edge between “connected” and “not connected.”

Why putty is the perfect troublemaker

Here’s where g-putty gets extra interesting: putty is not a simple material. It’s viscoelastic, which is a fancy way of saying it acts a bit like a solid and a bit like a liquid (see "Ketchup and Oobleck and Slime, Oh My!"). If you pull it quickly, it resists. If you leave it sitting, it slowly relaxes and flows. That personality shows up in the electrical signal too. The sensor doesn’t only care about how much you stretch it. It also cares about how fast you did it, and how long you held it there. So you start getting questions like:

• Does the signal “bounce back” instantly, or slowly drift?
• If you stretch it the same amount twice, do you get the exact same signal?
• Can you tell the difference between a quick tap and a slow squeeze?

Those are not annoying complications. They’re the whole point. Real-world sensing is messy. Bodies are messy. Soft robots are messy. A sensor that only works under perfect conditions is not very helpful.

What could you do with a squishy sensor?

Once you have a material that turns motion into signal, you can imagine all sorts of uses:

• A soft patch that tracks breathing by measuring chest expansion
• A stretch sensor in clothing that follows knee or elbow movement
• A gentle “electronic skin” that notices touch and pressure
• Soft robotics where the robot can sense its own bending, without hard parts

And because the material is moldable, it invites playful engineering. You can shape it, embed it, or combine it with other soft materials. It feels less like building electronics and more like crafting.

Why I keep coming back to it

I love g-putty because it flips the usual electronics story. Instead of fighting softness, we use it. Instead of demanding perfect order, we take advantage of a network that is constantly rearranging itself. It’s a reminder that physics doesn’t only live in clean lines and polished surfaces. Sometimes it lives in a squishy blob that refuses to sit still.