The bounce test

It is an unusual sight - but it's one that makes sense.

A huge stack of mattresses has just been unloaded in front of a building at Kiel University.

It is the home of a research group that calls itself "Industrial Anthropology."

A truck comes here almost every week, loaded with fresh mattresses, wrapped in plastic foil, and made at factories all over the world.

"And what we do is comparative product testing," says researcher Norbert Vogt.

Walk inside

The first thing you notice inside is a machine with a thick and heavy wooden roller, kneading a spring mattress. The strong mechanical arm moves up and down, leaving distinct traces on the surface of the mattress - exactly where a person would sleep.

"This is a fatigue-test," explains researcher Ephraim Groß. "The roller pushes the mattress with a weight of 1,400 Newton meters, while it rolls from one side to the other 30,000 times."

The test is required for a mattress to meet Germany's industry standard, DIN EN 1957. It's designed to determine how much height a mattress loses over time through pressure.

First tests in the laboratory

But what makes a perfect mattress? For that we need to go into the next room.

It's here that scientists can study the shape of your spine.

"We measure the whole spine," says Groß, "from the head over the neck area to the breast kyphosis and the loins to the tailbone!"

The device looks scary. Small pegs stick out of a tall rack. The researchers push them against the spine - matching its curve.

"We then take a photo of the curvature and evaluate it metrically," says laboratory head Norbert Vogt.

On a test bed

The researchers then compare the shape of the spine while standing to the shape of the spine while lying in bed.

For this test, a mattress lies on a metal frame. From below, numerous sensors measure the form of the mattress. All of them are connected to a computer.

"We push the sensors to the surface of the mattress. When somebody lies down on it and presses against it, the surface deforms. And we measure the depth of subsidence," Vogt says.

Two lines are now displayed on a monitor as curves: a red line shows the spine while standing, a blue line shows it while lying. The researchers use this to see the differences between the two lines and at which points the mattress should be softer or harder.

"Here we can see very clearly that our test person is exerting the most pressure around the area of the pelvis," says Groß. "Ideally, they should choose a mattress that has a harder zone, precisely here."

Norbert Vogt and his team can connect up to 300 sensors for the test.

"Usually we do that with more valuable 'zone mattresses.' It is our aim to adjust the different zones of the mattress in such a way that it meets individual needs."

A test for almost every type of mattress

In theory you can run such tests on all kinds of mattresses. The scientists from Kiel can even deal with futons from Japan and China - simple mats filled with cotton, wool or other fibers.

But there are two exceptions: "Waterbeds and air mattresses! We can't test them, because they would burst!"