has partnered with the engineering talent at DepthSight Innovations to develop state-of-the-art proprietary mattress testing tools that help consumers better understand how their mattresses will perform. We are proud to be the first independent and free service that provides these kinds of objective metrics. These tools go beyond the industry standard assessment of “soft” and “firm”. Read on to discover just what new testing Sleepsherpa is providing.

The Tests

The first test we perform is the free weight drop. We drop a whopping 220 pounds on the mattress to see how it responds. We are not aware of anyone else who does a test like this, and it can teach us a lot.

Not all mattresses bounce the same

The second test we perform is the firmness test. We slowly add more force the mattress and record force as well as travel as the circular plate sinks further into the mattress. While this test is not as exciting as dropping all 220 pounds at once, it too can teach us a lot about the characteristics of the mattress. Read on to learn more details about the six metrics we pull from these two tests.

The Metrics

The first three metrics come from the firmness test, where we slowing increase the force on the mattress. Let’s see what we can learn from this test.


Perhaps the number one question a mattress buyer will have on their mind is how firm the mattress is. We calculate the firmness using a method straight from ASTM 1566. It’s pretty simple, the less a mattress deflects with 175 lbs on it, the higher the firmness rating will be.

Surface Firmness

The firmness metric tells you a lot about how a mattress will feel for you, but it is a major over-simplification. Many memory foam mattresses feel more firm with light loads than with higher forces, while many spring mattresses get stiffer with more force applied. Most people also won’t exert 175 pounds on such a small surface while they are sleeping. That’s why at Sleep Sherpa we also report the “surface firmness.” Rather than calculate the firmness with 175 lbs, surface firmness is the value with just 40 pounds on the mattress.

Firmness test graph
The soft memory foam mattress has a lot of memory compared to the stiffer spring mattress. The composite mattress has some memory and is about the same stiffness as the spring mattress. Notice that both mattresses with foam have a higher surface firmness than the spring mattress when being loaded.

You may notice in the graph above that each curve actually consists of two lines that meet at the top and the bottom. Each curve looks sort of like a crescent moon. The first of these lines is the loading path, where the plate is moving into the mattress. The second line is the unloading path, where the plate is being lifted from the mattress. The difference in these two curves is called “hysteresis.” Hysteresis is just a technical way of saying “memory.” A mattress with a lot of memory will look like a fuller moon, while a mattress with very little memory will look like a very thin sliver. We have a proprietary way of measuring this memory and reporting it as the memory index.

Firmness, surface firmness, and memory are the three metrics we pull from the firmness test. Let’s take a look at what can be read from a drop test.

Impact Force

When you plop down on a mattress at night you might expect to bounce a little bit. That’s just what happens with most spring mattresses. Some cheap spring mattresses will even cause you to feel a large force, almost three times your own weight, when the mattress “bottoms out”. The impact force is simply the force you will feel on your bottom when you sit on the mattress.


In addition to the peak force, we can also measure how many times you might bounce and for how long you might bounce before the mattress absorbs your energy. We use a proprietary method to derive an unbiased bounciness index value.

Graph of drop force
The cheap store-bought spring mattress bounces at least 9 times for over 4 seconds. The memory foam mattress bounces for just about 1 second.
Partner Shake

Maybe you don’t worry too much about how you bounce in the bed, but your sleeping partner certainly will not want to feel the bed move when you are rolling around at night. That’s why we came up with the partner shake metric. We measure the movement of a controlled weight at a controlled distance from the drop location. From that movement information, we can tell how long and how much your partner will shake when you come to bed late after a marathon binge viewing of your favorite TV show.

Partner shake from a dropped weight
The partner experiences nearly 0.7 Gs of acceleration on the cheap spring mattress. At 1.0 Gs they could experience weightlessness. Yikes, that will make thier stomach churn!

More Tests are Coming

The team at Sleepsherpa and DepthSight are not planning to stop with force-based testing. A new tool on the horizon is one that will measure how well a mattress breathes. Traditional breathability metrics rely on measuring forced air flow rates, but who tries to breathe through their mattress? What matters is moisture transfer, and that’s what Sleepsherpa is going to measure. We are also developing a heat transfer test. Standby for updates. Click here for more information on Sleepsherpa and the technical staff at DepthSight.

Not all of the mattresses reviewed have gone through these tests but we are constantly updating our findings as new tests are done. Click Here for listing of mattress reviews.