The average person spends roughly a third of his or her life asleep. If you live to be 75 years old, that's 25 years on a mattress.

But that quarter-century is nothing compared with the amount of time you could spend configuring the queen-sized Reverie Dream Supreme II Hybrid Sleep System before you even lie down.

This $3,500 foam mattress, which performed well in CR's latest mattress tests, is unique in that allows users to customize the firmness by rearranging foam cylinders that act like bedsprings (shown below). There are 204 of them in the queen-sized model we evaluated. The individual springs are made of varying densities of foam, color-coded for levels of firmness. There are 64 pink cylinders (extra soft); 60 blue cylinders (soft); 50 green cylinders (medium); and 30 yellow cylinders (firm). To move them, you just slip them through a braid of webbing.

The Reverie Dream Supreme foam mattress has cylinders of different firmness that you can rearrange
You can adjust the firmness of the Reverie Dream Supreme II foam mattress by rearranging the color-coded foam cylinders, which serve as bedsprings.

For example, if you prefer a soft mattress, you can group pink and blue springs where your head and torso rest and use the firmer springs to fill in the outer slots. And of course, if you sleep with a partner, you can configure each half of the mattress differently.

CR tested the Reverie mattress in three different factory configurations: firmmedium, and soft, and each earned a different overall score among the more than 50 foam mattresses in our ratings

The Foam Factorial

The Reverie mattress is the only bed we know of with this customizable system. With all these slots—so many possibilites—we started to wonder: Just how many different permutations are there? We asked Chris Regan, a CR senior test engineer who oversees mattress testing, to crunch the numbers.

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WARNING: If you don't like math, skip to the next section.

Regan began with the total number of slots, or starting points, for the springs in the Reverie mattress.

“Start in the upper left corner and place one of the 204 cylinders," he said. "Now you have only 203 to pick from for the next spot, and so on, down to 1. Multiplying all of these numbers together is called a factorial."

But you don't have 204 different choices for each slot. There are really only four—one of each firmness (64 pink, etc.), and we needed to account for that limitation in the formula.

“Let's look at that first location again and place a pink cylinder there," he said. “In the second location, you have only 63 pink cylinders left to pick from.” That means we needed more of these factorials, and we needed to divide them out of the original 204 factorial.

So with 204 factorial as the numerator (the number above the dividing line), the denominator (below the dividing line) is the factorials for four colors of springs multiplied together.

What Does It All Mean?

“If you took the age of the earth in seconds, you’d still be far short of the number of combinations,” he says. “If you took how many cells are in the human body—roughly 37 trillion—then multiplied that by the number of people in the world, you’d still be far short of how many combinations this mattress offers.”

There you have it: A consumer could configure the Reverie mattress every second of every day until he or she dies and still wouldn’t scratch the surface of possible arrangements. So much for getting to bed early.

But is having such a gargantuan number of combinations beneficial? “Sure, theoretically you can configure this mattress many different ways,” Regan says. “But in practice, can you really?” 

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Doing the Math on the Reverie Mattress