1. Good Cushioning Keeps the Jolt Below What the Object Can Take
When a box lands on the floor, the damage does not come from the fall itself. It comes from how suddenly the box stops. A sudden stop means a large change of speed in a very short time, which engineers call a high acceleration (a stop is a negative acceleration, often called deceleration). The same object dropped from the same height onto a pillow stops more slowly, because the pillow squashes and stretches the stop over more time, so it experiences a smaller jolt.
Packaging engineers measure that jolt in "G," where 1 G is the ordinary pull of gravity. Every product has a limit: the largest jolt it can take before something breaks. Engineers call this limit the product's fragility, and it is one of the first things they define when designing a package, along with the drops the box is likely to suffer on its journey.[2] A heavy steel tool might shrug off a jolt that would crack a glass bulb.
So the job is not "make it soft." The job is: whatever drop is expected, keep the jolt that reaches the object below its limit. According to the 2025 study cited here, the strongest stress the cushion may be allowed to carry follows from the fragility of the protected object, and the best foam is the one that does the job most efficiently at that level.[1]
2. Engineers Test Padding by Dropping Weights On It and Drawing a Graph
How do you find out what a pad can really do? You test it. In a standard method, a weight is dropped onto a sample of the cushioning from a set height, and sensors record the peak acceleration, the biggest jolt during the impact. The test is repeated with heavier and lighter weights.[1]
The results are drawn as a cushion curve. Along the bottom goes the static stress: the weight of the object divided by the area of padding that supports it. Up the side goes the peak acceleration.[1] Separate curves are made for each thickness of padding and each drop height. A packaging designer then looks for a point where the curve stays below the product's fragility limit.
Here is a simple way to picture it. Imagine standing on a thick mattress with your whole foot, versus on the same mattress with only the tip of a pencil: the same weight pushes much harder on the small spot. That is why the weight is divided by the supporting area, and why a wider pad can protect something better than a narrow one of the same material.
3. A Pad That Is Too Thin, Too Hard or Too Overloaded Can Still Let the Jolt Through
A cushion curve usually dips and then rises again, and that shape explains the surprise at the heart of this article. The 2025 study describes a foam that has a most efficient working stress, and notes that at higher stress the foam is squashed until it has nothing left to give, a state engineers call densification, after which it no longer cushions well.[1]
You can feel the idea with a simple picture. If a very light object lands on a stiff pad, the pad hardly squashes, so the object almost bounces off a hard surface and the jolt stays high. If a very heavy object lands on a thin soft pad, the pad squashes completely and the object hits the hard layer underneath. In between there is a sweet spot where the pad squashes a good part of its thickness and slows the object gently.
That is why the same piece of padding can protect a small gadget well and fail with a bigger one. And it is why a repair after a failed drop test is not simply "add more padding": the designer goes back to the thickness and the area that touches the object and checks the curve again.
4. Bubble Wrap, Foam and Paper Each Squash Differently, So Each Suits Different Jobs
Most cushioning materials work by trapping air or by bending in a controlled way, but they behave differently under load.
Bubble wrap. This began as a failed wallpaper. In 1957, the inventors Alfred Fielding and Marc Chavannes ran two plastic shower curtains through a heat-sealing machine, hoping for a textured wallpaper, and got a film full of trapped air bubbles. They patented the process and brainstormed more than 400 possible uses. Greenhouse insulation reached the market, but it was about as unsuccessful as the wallpaper.[3] Packaging was the idea that worked. According to Wikipedia, which gives this detail without a primary document in the text I read, the company was launched in 1960 and its first packaging customer was reportedly IBM, which is said to have used the sheets to protect its 1401 computer in shipping.[4] The Smithsonian article says the invention went on to revolutionize shipping.[3]
Expanded polystyrene foam. The white foam in appliance and electronics boxes is described by the North American industry association as "98 percent air" and as offering high shock absorption.[5] How a foam full of tiny trapped bubbles takes a hit is the kind of thing a cushion curve is used to check. This association represents the foam's makers, so treat its praise as a manufacturer's view.
Paper and cardboard. Some companies want to swap foam for paper to use less plastic. The curve idea shows why that is not a simple swap: each material has its own curve, so a new material means new tests for each product.[1] I did not find a head-to-head test showing that paper is better or worse than foam in general, so this article makes no claim either way.
5. At Home, the Same Rules Mean Filling the Gaps So Nothing Can Slide Around
You do not need a laboratory to use the idea. Choose padding that suits the object and the box. Fill the empty space so the object cannot slide or rattle, because with a gap, an object can move around and knock against the walls. Use enough, but not endless amounts: more padding also means more waste. These are common-sense applications of the ideas above, not rules from an official standard, so check your own postal service's packing page for its advice.
6. A Small Experiment With an Empty Box, and a Question to Take Away
Next time a parcel arrives, open it and look at the padding before you throw it away. What kind is it? How big is the gap between the object and the box? Is the object heavy or light, tough or easily broken? Try to explain why the packer chose that padding.
If you want to try a very gentle test with an adult, put a small bell or a pebble in a cardboard box and close it securely with tape. Make a second box with the same item wrapped in crumpled paper, also taped shut. Holding each box at knee height, gently let it drop onto a folded blanket or a bed, not the floor. Keep the boxes closed, and do not use anything fragile or sharp. Listen for the rattle and watch how the object moves. This is only a simple look, not a real laboratory test. Keep fingers clear and do not drop anything onto people or pets.
The question to take away: if a thicker pad is not always better, how would you test the best thickness for something you own?