Knee Pillow for Side Sleepers: Why to Use One and How to Choose
The short answerA knee pillow is a small pillow you place between your knees when you sleep on your side. It keeps your legs apart so your top knee doesn't drop forward and down, and your hips, pelvis and lower back stay in a straighter line. Look for one shaped to hug your knees, made of foam that doesn't flatten, with a strap that keeps it in place when you turn over.
In brief
- When you sleep on your side, your top knee tends to drop forward and twist your pelvis; the pillow spaces your legs and straightens things out.
- A good knee pillow hugs your knees, doesn't slip and keeps its shape over time.
- An adjustable strap helps it stay in place when you turn at night.
- The first week feels a bit odd; after that it becomes natural.
Why put a pillow between your knees when you sleep on your side?
A knee pillow keeps a gap between your legs so your body stays in a straighter line from your shoulders down to your knees. It's the simplest way to improve your side-sleeping position.
When you sleep on your side without one, your top leg tends to fall forward and down onto your bottom leg or the mattress. Your pelvis rotates with it, and your lower back stays twisted for hours. Many side sleepers wake up with stiffness in the hip or lower back and can't work out where it comes from.
With a pillow between your knees, your top knee rests on it instead of dropping. Your hips stay stacked one above the other, and your whole body settles into a more relaxed position.
Who is a knee pillow for?
It suits anyone who sleeps on their side, and it's especially worth considering if:
- You wake up with stiffness in your lower back or hips.
- You feel your knees pressing into each other at night.
- You already put a regular pillow between your legs and find it on the floor in the morning.
- You're pregnant and sleep on your side – after checking with your doctor.
How to choose a knee pillow
Three things decide whether a knee pillow works: its shape, its material and what keeps it in place.
| What to check | Folded regular pillow | Dedicated knee pillow |
|---|---|---|
| Shape | Flat, not shaped for knees | Hourglass shape that hugs the knees |
| Stability at night | Moves and falls when you turn over | Adjustable strap keeps it in place |
| Material | Filling that bunches up and flattens | Dense memory foam that holds its shape |
| Height | Changes through the night | Consistent, keeps a steady gap |
| Cleaning | Depends on the pillow | Removable, washable cover |
Pillow height
The pillow should fill the gap between your knees so your top leg sits at roughly hip width. A pillow that's too thin doesn't create enough space, and one that's too thick opens your legs too far.
What makes SleepAlign different?
The SleepAlign knee pillow was designed for exactly this: you place it between your knees when you sleep on your side.
- Hourglass shape: hugs your knees and doesn't slip.
- Adjustable strap: keeps the pillow in place even when you turn over.
- Dense memory foam: doesn't go flat after a couple of weeks.
- Breathable cover: removable and washable.
- In the box: pillow, cover, strap and instructions.
It's also suitable during pregnancy, to support the pelvis when sleeping on your side, after checking with your doctor. If you're looking for full-body support, read about the U-shaped pregnancy pillow too.
How to position the pillow correctly
Lie on your side, slip the pillow between your knees and fasten the strap. It takes less than a minute.
- Lie on your side with your knees slightly bent.
- Place the pillow between your knees so the upper hollow supports your top knee.
- Fasten the strap comfortably – not tight.
- Check that your knees and ankles are roughly stacked one above the other.
What happens in the first week?
In the first week the pillow feels strange, and that's expected. After a few nights it becomes natural, and many people don't want to sleep without it.
Common mistakes to know about
Most disappointments with knee pillows come from a few small mistakes that are easy to fix.
- Fastening the strap too tight: the strap is there to keep the pillow in place, not to press on your leg.
- Placing the pillow too high: it belongs between your knees, not between your thighs.
- Giving up after one night: your body needs a few nights to get used to a new position.
- Forgetting your ankles: if your feet fall onto each other, bend your knees a little more so your legs rest in one line.
What about the pillow under your head?
A knee pillow straightens the lower half of your body, but the straight line needs to continue up to your head. If your head pillow is too low or too high, your neck stays tilted.
Side sleepers need a higher head pillow than back sleepers, one that fills the space between shoulder and ear. The memory foam CervaCurve neck pillow offers two heights: a lower side for back sleepers and a higher side for side sleepers. Read more about choosing a head pillow in our guide to choosing a pillow for your sleep position, and find more products in the Neck & Sleep collection.
Not sure which pillow is right for you? Email us at hello@getxneex.com – real people answer.
Frequently asked questions
Should I sleep with a pillow between my knees?
If you sleep on your side, a knee pillow is a simple way to keep your hips, pelvis and lower back in a straighter line. Without one, your top knee tends to drop forward and rotate your pelvis. Many people feel more comfortable after a week of getting used to it.
How do you put a pillow between your knees?
Lie on your side with your knees slightly bent, place the pillow between your knees so the upper hollow supports your top knee, and fasten the strap comfortably, not tight. Check that your knees and ankles are roughly stacked one above the other.
Is a knee pillow suitable during pregnancy?
The SleepAlign pillow is also suitable during pregnancy, to support the pelvis when sleeping on your side. Check with your doctor before using it. If you want support for your belly, back and neck together, consider a full-body pregnancy pillow.
What if the pillow falls out at night?
A folded regular pillow tends to shift and fall when you turn over. A knee pillow with an adjustable strap stays snug against your leg even when you move. Fasten the strap comfortably so it holds the pillow in place without pressing on your leg.
How long does it take to get used to a knee pillow?
In the first week the pillow feels strange, because your body is used to a different position. After a few nights it usually becomes natural. Give it a week or two before deciding whether it suits you.
How do you clean a knee pillow?
The SleepAlign pillow's breathable cover is removable and washable, so you can wash it separately and put it back on. Air out the pillow itself, made of dense memory foam, from time to time, and only put the cover back on when it's completely dry.
More from the Knowledge Center
How to choose a pillow for your sleep position – and when to replace it →Ergonomic neck pillow: who it suits and how to choose the right height →U-shaped pregnancy pillow – how to sleep with it, step by step →All articles →This article is general information and is not a substitute for medical advice.