Winter pool covers are essential for protecting your swimming pool during the off-season, preventing debris buildup, freezing damage, and chemical imbalance. However, pool owners often debate one specific maintenance tip: do you really have to put a pillow under a winter pool cover? This seemingly small question has significant implications for your pool’s health, and the answer depends on various factors—from your climate to the type of pool cover you use.
In this detailed article, we’ll explore the science behind ice expansion, the roles of a pool pillow, and whether it’s truly necessary for your specific pool. We’ll also look at alternatives, installation tips, and common mistakes to help you make an informed decision.
Understanding the Purpose of a Winter Pool Cover
Before diving into the “pillow under winter pool cover” debate, it’s crucial to understand what a winter pool cover does. A winter cover—also known as a safety cover or solid cover—is designed to:
- Prevent debris like leaves, dirt, and animals from falling into the pool
- Protect the pool structure from freezing temperatures and expansion from ice
- Control algae growth by limiting sunlight exposure
- Maintain chemical balance by reducing evaporation and water dilution
However, while these covers are robust and tightly fitted, they’re not foolproof in combating all the challenges of winter—if not properly maintained.
Why Pool Owners Use a Pillow Under a Winter Cover
A pool pillow is a simple yet ingenious tool in winter maintenance. It is typically a large inflatable device—often made of durable vinyl—that is placed in the center of the pool before the cover is secured. The main purpose of this pillow is to act as a buffer for ice expansion.
The Science Behind Water Expansion and Ice Damage
Unlike most substances, water expands when it freezes. This expansion can exert immense pressure on your pool walls and floor. In enclosed conditions, ice can push upward and outward, potentially damaging liners, tiles, coping, and even concrete structures.
A pool pillow works by creating an air space in the center of the pool water. When water freezes from the cover downward, the pillow allows the ice to expand upward into the empty space, rather than pressing into the pool walls. This method is especially critical in in-ground pools, which are more vulnerable to expensive structural damage.
How the Pillow Reduces Hydrostatic Pressure
Sometimes, groundwater rise can cause a problem known as hydrostatic pressure, which pushes up on the pool from beneath. While this is a separate issue from freezing, it’s worth mentioning because a pool pillow can create space for such movement—though it’s not primarily designed for this. The primary function remains ice expansion prevention.
Is a Pool Pillow Absolutely Necessary?
The short answer is: it depends. Factors like climate, pool type, cover type, and water level all influence whether a pillow is needed.
Climate Considerations
If you live in a temperate climate where freezing is rare or light, the need for a pool pillow may be minimal. However, in regions that experience consistent below-freezing temperatures, a pillow becomes highly beneficial, even essential for many pool types.
Pool Type
- In-ground pools: Particularly vulnerable to ice damage, so a pillow is recommended.
- Above-ground pools: Often designed to be partially or fully drained for winterization. In these cases, pillows may not be as necessary if water levels are significantly lowered.
- Pools with solid winter covers: Covers that do not allow water to drain can trap ice, making pillows more beneficial.
Pool Cover Type
The type of winter cover you use significantly affects this decision:
| Cover Type | Does It Require a Pillow? | Why? |
|---|---|---|
| Solid Winter Covers | Recommended | They prevent water evaporation and trap ice, increasing pressure. |
| Mesh Winter Covers | Usually Not Needed | They allow rain and snowmelt to drain through, reducing ice buildup. |
| Automatic Safety Covers | Sometimes | Well-designed covers may have built-in slack, but pillows help with freeze protection. |
Bottom line: A pillow is most crucial for in-ground pools with solid covers in cold climates. In less severe conditions, pool owners may choose to forgo it—but only after careful consideration.
What Happens If You Don’t Use a Pillow Under the Cover?
Failing to use a pool pillow can lead to a range of problems, some immediate and others only noticeable months later when warmer weather returns. Here are the most common issues:
Ice Expansion and Structural Damage
Without a pillow, ice forms from the bottom up (since covers restrict sun exposure), creating layers that push outward. This can pop tiles, crack the pool shell, and damage the bottom of the pool. In some cases, the edges of the pool deck may lift or crack.
Damage to the Pool Cover
When ice forms without an expansion cavity, the pressure can cause ripping, stretching, or misalignment of the cover—reducing its lifespan and effectiveness for future winters.
Costly Repairs
Even a small crack can lead to expensive pool repairs. Fixing a damaged liner or addressing a compromised pool shell may cost thousands of dollars, far beyond the $30–$100 price tag of a quality pool pillow.
Chemical Imbalance Complications
Pressure cracks or cover failures can allow debris and contaminates into the pool, making opening the pool more labor-intensive for the next season.
Alternatives to Using a Pool Pillow
If you’re wondering whether there are alternatives to the traditional pool pillow, the good news is: yes. However, these options may not completely replace the purpose of a pillow in areas with true freezing conditions.
Proper Water Level Adjustment
Some pool owners lower the water level to several inches below the skimmer before covering. The idea is that this extra space allows for upward ice expansion without contacting the cover.
However, this method alone is not foolproof, especially if snowmelt increases the water level or if ice forms thickly on the pool’s surface.
Using an Air Pillow Substitute
In a pinch, some pool owners use a pool noodle or inflated pool float instead of a traditional pillow. While not as effective, these can mimic the effect by displacing water and allowing some space for expansion.
Winter Covers with Built-in Air Blisters
Some premium pool covers on the market now come with built-in air bladders that act like a pillow. These are especially useful for large in-ground pools and provide a neat, permanent-looking solution.
How to Correctly Use a Pool Pillow
If you’ve decided that a pool pillow is necessary for your winter pool maintenance, proper installation is key. Here’s a step-by-step procedure for an effective setup:
Step 1: Prepare Your Pool
Before applying the cover:
- Balance your pool chemicals
- Add winter algaecide and stain control products
- Close the skimmer, return lines, and drain the pump if required
Step 2: Place the Pillow in the Center
Place the inflatable pillow in the center of the pool, tying it to an anchor chain or secured cover straps. Do not just let it float freely—it needs to remain in the middle.
Step 3: Secure the Pool Cover
Lay the cover over the water, ensuring it’s evenly centered and the edges are tucked. Use water bags, anchors, or spring brackets to secure it firmly. Make sure the pillow stays under the cover and doesn’t rise above the edges.
Tips for Securing a Pillow and Cover:
- Use a mesh or solid winter cover according to your climate
- Use tie-down straps or ropes to help keep the pillow in place
- Inspect the cover regularly after snowfall or rain to ensure pressure is distributed
Common Mistakes to Avoid When Using a Pool Pillow
Forgetting about the pillow or applying it incorrectly can lead to the very issues you’re trying to prevent. Here are some of the most frequent errors:
Placing the Pillow on the Wrong Side
Make sure the pillow is placed under the cover before you completely secure the cover. It cannot sit on top of the cover and be effective.
Using a Deflated Pillow
The pillow must be fully inflated to provide air space. Under or overinflating can be equally harmful. Underinflated pillows won’t create sufficient space; overinflated ones may pop.
Leaving the Pillow Untethered
Pool pillows left to float freely often move off-center, reducing effectiveness. Always tether or anchor the pillow to keep it in place.
Ignoring Climate Conditions Post-Installation
If your area receives heavy snowfall, it’s vital to regularly remove snow weight from the center of the cover. Too much weight can compress the pillow and negate its purpose.
When Can You Skip the Pool Pillow?
There are specific scenarios where a pool pillow may be unnecessary or even counterproductive. Here are some examples when you may think twice before using one:
You Live in a Warm Climate
If the temperature in your area doesn’t drop below 32°F (0°C), freezing will not occur. As a result, ice expansion is not a concern, and a pool pillow becomes unnecessary.
You’re Using a Mesh Cover
Mesh covers allow rainwater and melted snow to filter through, significantly reducing the chance of solid ice formation. This gives the water below the cover room to expand without creating structural pressure, making pillows optional.
You Drained the Pool Below Freezing Level
In some cases, above-ground or inflatable pools are entirely or partially emptied over winter. If the water level is low enough to prevent freezing, a pillow is not required.
You Have an Insulated Covering System
High-end pool covers may include insulated material or dual-layer systems designed to reduce the risk of freezing. While rare, these options may negate the need for a pillow.
Conclusion: Does Your Pool Need a Pillow Under the Winter Cover?
The use of a pool pillow is generally a sound investment to prevent costly winter damage. For in-ground pool owners in cold climates, skipping the pillow is a risk not worth taking. Pool pillows are a small, relatively inexpensive item that can save hundreds or thousands of dollars in repairs later on.
Always base your decision on factors like:
- Climate
- Cover type
- Premium cover materials or alternative systems
- Pool style and volume of water
Consult with a local pool professional for tailored advice if your situation is uncertain. In general, when in doubt, play it safe and use the pillow—it provides peace of mind and valuable protection for your long-term investment in your pool.
Why would you put a pillow under a winter pool cover?
Putting a pillow under a winter pool cover is often recommended to help prevent damage caused by the expansion of water as it freezes. When water in a pool freezes, it expands and can exert pressure on the pool walls and cover. A submerged pillow absorbs some of this pressure by acting as a flexible buffer, reducing the risk of stress-related damage to both the cover and the pool structure. This practice is especially important in regions where freezing temperatures persist for extended periods, making it a simple but effective step in winterization.
In addition to protecting the physical integrity of your pool, using a pillow helps maintain the balance of water pressure between the surface and the bottom of the cover. Without a pillow, freezing can cause the water to rise unevenly, potentially displacing the cover or even causing it to tear. While not every pool requires a pillow—especially depending on the specific winterization method used—it’s considered a best practice for in-ground pools with solid winter covers to ensure a smoother reopening in the spring.
Can you use any type of pillow for a winter pool cover?
Not all pillows are suitable for use under a winter pool cover. It’s recommended to use a specifically designed pool cover pillow, which is made to be durable and buoyant enough to handle freezing temperatures and shifting ice. These pillows are typically constructed from heavy-duty vinyl or other weather-resistant materials and are designed to float in place without puncturing the cover. Regular household pillows or air-filled cushions may not withstand the harsh winter conditions and could degrade or deflate, negating their protective purpose.
Pool cover pillows are generally hollow with a ribbed or accordion-style design, allowing them to compress under pressure and absorb the force of expanding ice. They also tend to be large enough to provide sufficient displacement and protection without easily shifting around in the pool. While it might be tempting to improvise with alternatives like beach balls or plastic jugs, these items may not perform as consistently and can risk damage to the cover or pool. Investing in a proper pool cover pillow is a small cost compared to potential repair expenses.
How many pillows do you need for a winter pool cover?
The number of pillows needed under a winter pool cover depends primarily on the size and shape of the pool. For an average-sized in-ground pool (around 16×32 feet), it’s generally recommended to use one pillow for every 10 feet of length. This means a typical rectangular pool would require anywhere from two to four pillows to provide adequate pressure relief across the surface. Round or uniquely shaped pools may require fewer or differently positioned pillows to ensure even coverage.
Proper spacing of the pillows ensures that pressure from freezing water is evenly managed throughout the pool. If you use too few pillows, certain areas may be at risk of excessive pressure buildup, leading to damaged covers or pool structures. Conversely, using too many can cause unnecessary crowding and interfere with the placement and tension of the cover. Always consult the manufacturer’s recommendations or a pool professional if unsure, especially for unusually sized or custom-designed pools.
Is a pillow necessary for all types of winter pool covers?
A pillow is not always necessary for all types of winter pool covers, especially if you’re using a safety cover or a mesh cover that allows water and snow to pass through naturally. In these cases, the pressure from frozen water is mitigated naturally because the water isn’t trapped beneath an impermeable surface. However, for solid winter covers—which are designed to prevent debris and water from entering the pool during the off-season—a pillow is crucial for absorbing the stress caused by ice expansion.
Solid covers trap water on the pool surface, allowing for a layer of ice to form during freezing temperatures. Without a pillow, the ice can expand uniformly and exert damaging pressure against the pool walls and cover. Safety covers, often secured tightly and anchored to the deck, offer structural support and distribute pressure more evenly, reducing the need for a pillow. Ultimately, whether or not a pillow is needed depends on the type of cover being used and the local climate’s severity.
What happens if you skip using a pillow under a winter pool cover?
Skipping the use of a pillow under a solid winter pool cover can lead to a number of issues, particularly in colder climates where freezing is common. The biggest risk is that ice forming on the pool surface can expand and create significant pressure on the cover and the pool structure. This pressure may cause the cover to bulge, tear, or even damage the pool walls, especially in in-ground pools with rigid structures that cannot easily absorb this force.
Additionally, skipping this step may result in water overflow or shifting of the cover, which can lead to debris accumulation and additional cleaning challenges in the spring. If the cover is displaced or damaged during the winter, rain and snowmelt can enter the pool and raise the water level, increasing the risk of water staining, algae growth, and chemical imbalance. These issues complicate pool opening and maintenance, making the small effort required to add a pillow a worthwhile investment in the long run.
How do you install a pool cover pillow correctly?
Proper installation of a pool cover pillow is simple but crucial for ensuring optimal protection during the winter months. Start by submerging the pillow in the pool before placing the cover. Allow it to float freely for a brief period so that it fills with water and displaces any air that could cause it to shift or become unstable. Once settled, gently push the pillow beneath the winter cover, positioning it in the center of the pool or strategically spaced depending on the pool’s size and the number of pillows used.
After placing the pillow(s), spread the cover as evenly as possible over the pool surface and secure it according to the manufacturer’s instructions, using water bags, anchors, or clips. Make sure the cover is taut enough to prevent water from pooling in certain areas, but not overly tight that it restricts some movement for ice expansion. The pillow should be fully submerged and centered under the cover to provide effective pressure relief. Check the setup after installation to ensure everything is secure and adjust if necessary before consistently cold weather arrives.
Where should the pool cover pillow be placed in the pool?
The ideal placement for a pool cover pillow is near the center of the pool or evenly spaced throughout the pool if multiple pillows are used. This positioning allows for even pressure distribution across the water surface as ice forms and expands during winter temperatures. For rectangular pools, placing a pillow approximately every 10 feet ensures that pressure does not disproportionately build in any one area, minimizing the risk of damage to the cover or pool walls.
Avoid placing the pillow too close to the edges or the skimmer, as this can cause unnecessary stress on fittings and pool components. Each pillow should remain fully submerged and not touching the sides or bottom of the pool to work effectively. Once the pillow is in position, centering it beneath the corresponding portion of the cover helps balance the forces of freezing water and prevents the cover from distorting or lifting. Correct placement allows the pillow to do its job efficiently and helps maintain the integrity of your winterized pool.