A gap between a king mattress and its headboard can swallow pillows, remotes, and other bedtime essentials. A mattress extender fills that space, but the right style depends on how wide the gap is and whether you want a simple filler or a wedge that can double as back support. These five options range from slim, fixed-size fillers to adjustable wedge pillows, so check the product dimensions against your bed before choosing.
Quick Comparison
| Product | Design | Standout feature | Best suited for |
|---|---|---|---|
| DEEPSHARK Bed Gap Filler | Foam filler with linen cover | 16 size options; removable, washable cover | Shoppers who want a straightforward filler with size choices |
| DEEPSHARK Mattress Gap Filler | Foam filler with silk-and-cotton-blend cover | Three listed widths: 4, 6, and 8 inches | Filling a gap with a known width |
| FeelAtHome King Bed Gap Filler | Adjustable foam wedge | Designed for gaps from 0 to 8 inches; side pocket | People who want a gap filler that can also support lounging |
| Homemate King Bed Wedge Pillow | Triangular foam wedge | 6-by-10-inch profile; side pockets | Those who want a more substantial wedge and extra back support |
| WUIOYNF Mattress Extender | Long, slim foam filler | King option measures 78 by 2 by 8 inches | King beds needing a simple, low-profile filler |
Our Picks: Best Mattress Extender For King Bed reviews
1. DEEPSHARK Bed Gap Filler: A Flexible, Washable Option
This DEEPSHARK filler is a foam insert designed to sit between the mattress and a headboard or wall. The listing describes 16 size options for king beds, which gives you more choices than a product offered in just a few widths. Check the dimensions of the specific option carefully, since the number of choices alone does not tell you which one will fit your bed.
The insert uses high-density 45D sponge, and its linen cover is removable and washable. That makes the design practical for a spot that may collect dust or come into contact with bedding. The maker says the compressed foam can take 48 to 72 hours to expand after unpacking, so allow time before judging its final shape and fit.
Compared with the adjustable wedges below, this is a more direct solution: it is intended to close the headboard-to-mattress gap, not serve as a large lounging pillow. It may also work as a sofa back support cushion, according to the product description. Its main limitation is that buyers need to match a listed size to their actual gap rather than relying on the word “king” alone.
Pros:
- Offers 16 size options for king beds
- Uses 45D foam, according to the listing
- Removable linen cover is described as machine washable
- Can also be used as a sofa back support cushion
Cons:
- Needs 48 to 72 hours to fully expand after unpacking
- You’ll need to check the chosen size against your bed’s gap
Verdict: Choose this DEEPSHARK if you want a washable, conventional gap filler and value having many size options to compare.
2. DEEPSHARK Mattress Gap Filler: Three Widths for Different Gaps
This DEEPSHARK model focuses on gap width. It is offered in 4-, 6-, and 8-inch widths, so you can choose based on the space between your mattress and headboard or wall. Measuring that space before ordering is especially important here: a filler that is too narrow may leave an opening, while one that is too wide may not sit neatly in place.
The filler uses resilient 45D foam and has a removable, washable silk-and-cotton-blend cover. The description says the foam is intended to fit the mattress seams and retain its shape with use. It is also presented as a flexible option for other gaps or as a mattress extension filler, though its main use is closing the space behind the bed.
One point to plan for is expansion time. The listing gives a broad recovery window of 24 to 115 hours after unpacking, depending on how long the product was compressed. That makes this a less immediate setup than a ready-to-use cushion. Its clearly listed width options are helpful, but the listing does not provide every dimension in the supplied information, so confirm the selected size on the product page.
Pros:
- Three width options: 4, 6, and 8 inches
- Made with 45D foam, according to the description
- Removable cover is listed as machine washable
- Can be used for different bed-gap configurations
Cons:
- Expansion may take 24 to 115 hours
- Measure your gap and confirm the full dimensions before ordering
Verdict: This is a sensible pick when you have measured the gap and want to choose among a few clearly stated widths.
3. FeelAtHome King Bed Gap Filler: An Adjustable Wedge for Lounging
Unlike a narrow insert made mainly to close a seam, the FeelAtHome is a wedge pillow designed to cover gaps from 0 to 8 inches. Its shape is intended to provide coverage along the mattress edge while helping keep pillows and other items from slipping into the space. The listing describes a non-slip bottom, which may help the wedge stay in place, though a good fit still depends on your bed setup.
This option has more uses beyond filling a gap. It can be positioned as a pillow or back support while reading or watching TV, and it has a side pocket for small items such as glasses or a phone. The cover is removable and washable. The foam is described as high density, and the maker recommends letting it expand for 24 to 48 hours after removing it from its compressed packaging.
The trade-off is that a wedge pillow is a larger, more multipurpose piece than a simple gap strip. That can be useful if you want back support, but it may be more than you need if your only goal is to stop small items from falling behind the bed. It is listed in four bed sizes, including king, so confirm that the selected version is right for your mattress.
Pros:
- Designed to fit gaps from 0 to 8 inches
- Non-slip bottom and high-density foam are specified
- Side pocket provides a place for small items
- Can double as a reading or back-support pillow
Cons:
- Bulkier than a basic gap filler if you do not need a wedge pillow
- Needs 24 to 48 hours to expand after unpacking
Verdict: Pick the FeelAtHome if you want one product to cover the bed gap and provide extra support for sitting up.
4. Homemate King Bed Wedge Pillow: A More Substantial Profile
Homemate’s triangular wedge is designed to sit between a headboard or wall and the mattress. The listed profile is 6 by 10 inches, and the maker says it can fill gaps from 0 to 8 inches. That taller shape may suit shoppers who want a more noticeable cushion at the head of the bed, rather than a slim strip that is less visible.
The wedge uses 25D foam, described as resilient, and its breathable cover has reinforced pockets on both sides. Those pockets make small items easier to keep nearby. The cover has a zipper and is listed as machine washable. The product description also says the wedge can be used as a back support or alongside ordinary pillows for head and shoulder elevation.
This shape offers more support potential than the two DEEPSHARK gap fillers, but it also takes up more space. It is sold in multiple length sizes for different beds, so make sure the king option matches the width of your mattress. The compressed foam may need 24 to 48 hours to regain its shape before you can judge how it fits.
Pros:
- 6-by-10-inch profile is designed to cover gaps up to 8 inches
- 25D foam and a breathable cover are specified
- Side pockets are available on both sides
- Can also work as back support or a pillow wedge
Cons:
- Its larger profile may be unnecessary for a narrow gap
- Needs 24 to 48 hours to regain its shape after unpacking
Verdict: Choose Homemate if you want a taller, multipurpose wedge with storage pockets, and have room for its fuller profile.
5. WUIOYNF Mattress Extender: A Slim, Full-Width King Filler
The WUIOYNF is a long, slim mattress-to-headboard filler. Its king version is listed as 78 inches wide, 2 inches high, and 8 inches deep. That fixed profile makes it a straightforward option to consider if you need a filler across the width of a king bed and the listed dimensions match your setup.
The product description specifies high-resilience foam beneath a linen cover, with a zip-off cover that is machine washable. The listing says the filler is available in eight sizes, with widths from 39 to 78 inches for different bed sizes. It also claims a precision-cut tolerance of plus or minus 0.3 inches; treat that as the maker’s stated specification and verify the size you select before ordering.
Compared with the wedge pillows, this model is more focused on closing the gap than providing back support. Its 2-inch height gives it a lower profile, but that may not cover a larger vertical space as fully as a taller wedge. It can also be used as a wall-to-bed buffer or sofa armrest, according to the description.
Pros:
- King version is listed at 78 inches wide
- Eight size options cover listed widths from 39 to 78 inches
- Zip-off linen cover is described as machine washable
- Low-profile design may suit shoppers who prefer a simple filler
Cons:
- The 2-inch height may not suit a taller gap
- Check the fixed dimensions carefully before choosing a size
Verdict: Consider this WUIOYNF model for a low-profile, full-width solution when its listed 78-by-2-by-8-inch king size fits your gap.
How to Choose a Mattress Extender for a King Bed
Measure the gap, not just the mattress
Measure the space between the mattress and the headboard or wall where the filler will sit. Check the gap at more than one point if the headboard or wall is not perfectly straight. Compare your measurements with the filler’s width and height, not only its bed-size label. A product described as king-size may still come in several dimensions or configurations.
Choose between a simple filler and a wedge pillow
A slim filler is usually the more direct choice when your main aim is to close a gap and keep items from slipping behind the bed. A wedge pillow takes up more space but may also serve as a backrest or support while you read or watch TV. Think about whether you will use those extra functions, since a multipurpose wedge can be bulkier than needed for a small opening.
Match the profile to the size of the opening
Consider both the width of the gap and how tall or deep the filler needs to be. The WUIOYNF king option, for example, is listed as 2 inches high, while the Homemate wedge has a 6-by-10-inch profile. These shapes will sit differently against a mattress and headboard. Check all listed dimensions and choose a product that can cover your particular space without pushing awkwardly against the bed.
Look at the cover and cleaning instructions
A removable cover can make routine cleaning easier. The products here describe covers made from linen or a silk-and-cotton blend, and list machine washing for their covers. Check the specific care directions before laundering; the DEEPSHARK model with linen fabric, for example, advises low-heat tumble drying or air drying.
Plan for foam expansion
Several options arrive compressed and need time to expand before they reach their intended shape. The stated expansion periods vary: some descriptions suggest 24 to 48 hours, while one DEEPSHARK model lists a wider recovery window. Follow the instructions supplied with the product and give it the recommended time before deciding whether it fits well.
Decide whether extra features are useful
Side pockets can hold small items such as glasses, a phone, or a remote, while a wedge shape may provide extra support for sitting up. If you only need to block a gap, those features may not matter. If you expect to use the cushion for lounging, compare the wedge’s size and shape with the way you sit or sleep.
Frequently Asked Questions
What does a mattress extender do on a king bed?
It fills the space between the mattress and a headboard or wall. Depending on the design, it can help stop pillows and small items from slipping into the gap. Wedge-style models may also work as back support.
How do I know what size mattress gap filler to buy?
Measure the gap’s width, height, and length, then compare all three measurements with the product’s listed dimensions. Do not rely on the king-size label alone, since some options come in multiple sizes.
Can I use a bed gap filler without a headboard?
Some products are described for use between a mattress and a wall, including wedge-style models. Check the shape and dimensions before ordering to make sure the filler suits your bed’s position and the surface behind it.
How long should I wait for a compressed foam filler to expand?
Follow the instructions for the specific product. The options in this guide list expansion periods ranging from 24 to 48 hours to as long as 48 to 72 hours, with one description giving a broader 24-to-115-hour recovery window.
Are mattress gap filler covers washable?
The products here describe removable covers, and several specify machine washing. Care instructions differ, so check the product details and the label before washing or drying the cover.
Should I choose a wedge pillow or a narrow filler?
Choose a narrow filler if you mainly want to close the gap. A wedge pillow is a better fit if you also want a cushion for sitting up or lounging. Compare its profile with the available space so it does not feel oversized for your bed.
Final Recommendation
For a simple, washable filler with many size options, the DEEPSHARK Bed Gap Filler is a practical place to start. If you want a multipurpose cushion, consider the FeelAtHome adjustable wedge or the taller Homemate model. For a slim, full-width option, the WUIOYNF may suit your setup if its listed dimensions match your measured gap. In every case, measure first and allow compressed foam the time it needs to expand.