Bubbles up or Down on Solar Cover


The solar pool cover bubbles should face down toward the water when installed. This allows the bubbles to trap and retain heat from the sun’s rays within the pool water, creating a greenhouse effect that can raise your pool’s temperature by up to 15°F.

In this article, we will explore the reasoning behind why the bubbles on your solar pool cover should always face down toward the water, the science of how solar pool covers work, and the consequences of installing them the wrong way.

Before diving further into the correct bubble orientation, it is crucial to understand how solar pool covers work to keep your pool warm.

How Do Solar Pool Covers Work?

Bubbles on blue solar pool cover

Solar covers, sometimes called bubble covers or thermal blankets, are made of thousands of small, round plastic bubbles encased between top and bottom layers of plastic sheeting. It’s the bubbles that give solar covers their distinctive textured look.

When spread atop a swimming pool, these covers create an insulating barrier that leverages the sun’s radiant energy to heat the water. The bubbles work together to trap heat from sunlight during daytime hours and retain it in the pool water overnight.

This means your solar pool heater doesn’t have to work as hard or for as long to maintain the desired water temperature. As a result, you can reduce your energy consumption and lower your heating costs.

Here’s a closer look at the science behind this process:

Trapping Solar Heat

During daylight hours, the sun beams down on the solar cover, passing through the top plastic layer and heating the air trapped inside each individual bubble.

The bubbles act like miniature greenhouses, capturing and accumulating the sun’s thermal radiation within their domed shape.

This sunlight passes through the top plastic sheet and turns into heat when it strikes the darker-colored pool water below. The heated air becomes trapped in the bubbles, creating thousands of tiny hot pockets separated by thin plastic walls.

Transferring Heat to the Pool

Once heated by the sunlight, the hot air trapped in the pool blanket bubbles and transfers its warmth to the pool water, mainly through conduction. The bubbles sit directly on top of the water’s surface. This allows the trapped hot air to contact the water, efficiently conducting heat directly.

The layer of thousands of heated air bubbles essentially functions like a thermal pool blanket for the pool. The air bubbles provide high surface area contact between the heated air and water, facilitating excellent heat transfer.

Retaining Heat Overnight

After the sun goes down, the insulating bubbles play an important role – preventing newly gained heat from rapidly escaping into the night air.

The greenhouse effect of the solar cover bubbles enables pool water to stay around 8-10°F warmer on average compared to using no cover. Proper installation ensures the bubbles can work their heating magic to their full potential.

For all these benefits,

The bubbles must be oriented in the proper direction.

When facing the correct way, the thousands of bubbles harness and retain the sun’s heat. Flip the cover over, and it underperforms on one of its primary jobs.

What Is the Correct Orientation of Solar Pool Covers?

When installed, the bubbles on a solar pool cover should always face down toward the water. This is considered the proper orientation for optimal performance.

With the bubbles facing down into the pool, the cover can effectively trap heat from sunlight during the day and retain warmth in the water overnight.

Why Solar Cover Should Always Be ‘Bubbles Down’?

Solar Cover Should Always Be 'Bubbles Down'

Installing your solar cover with the bubbles facing downwards is essential for the cover to work as designed. Here’s a deeper look at why this orientation is so important:

Maximizing Solar Heat Absorption

With bubbles oriented downwards, they can directly trap and retain the sun’s thermal radiation throughout daylight hours. The bubble size is designed to readily capture and accumulate heat from sunlight passing through the top clear plastic layer.

Each individual pool blanket bubble allows solar rays to enter the pool while preventing the resulting heat from escaping. This enables the bubble wrap interior to reach high temperatures that warm the pool water.

Bubbles facing upwards cannot capture this warmth as effectively.

Creating an Insulating Barrier at the Surface

Thousands of bubbles facing the water create an insulating layer of trapped hot air at the pool’s surface. The direct contact allows for excellent heat conduction into the water.

The millimeter-thin plastic bubble walls separate the heated interior from the cooler exterior air.

This insulating barrier minimizes upward convection currents, forcing the pool’s accumulated warmth to remain near the surface, where it can raise water temperatures. Without bubbles down, heat readily escapes upwards.

Efficient Conduction for Daytime Heating

The sun’s rays heat the air trapped inside each bubble pocket during the daytime.

With bubbles facing down, this warmed air directly interacts with the water’s surface below. This allows for very efficient heat transfer from the hot air to the cooler water via conduction.

The bubbles provide a substantial surface area for heat conduction to occur. The thin bubble walls do little to inhibit heat from the high-temperature bubble interiors into the water. This is how the cover provides significant daytime pool heating.

Minimizing Nighttime Heat Loss

After sunset, the insulating layer of bubbles plays a crucial role in preventing radiant, conductive, and convective overnight heat losses. The bubbles act as thousands of miniature barriers keeping newly gained warmth from rapidly dissipating into the cool night sky.

The bubbles prevent warm pool water from rising and mixing with the cold air above (convection). They also inhibit the direct heat transfer from the water to the air (conduction). The bubbles absorb much of the infrared radiation emitted by the warm water, retaining it in the system (radiation).

Allowing Consistent, All-Day Heating

Thanks to the greenhouse effect and insulation provided by properly oriented bubbles, the pool experiences reliable, all-day heating. The water temperature remains significantly elevated around the clock rather than drastically dropping overnight.

This day-and-night heat retention enables the bubbles to leverage the sun’s peak intensity and sustained energy over many hours. Consistently warmer water can be maintained by trapping the sun’s daily heating potential.

Maintaining Comfortable Swimming Temperatures

Yong woman swimming in pool

An uncovered pool loses up to 70% of its accumulated daily heat after sunset through radiation, convection, and conduction. With bubbles facing down, this undesirable heat loss is slashed substantially.

The insulating bubbles keep the pool’s water temperature in a comfortable swimming range even as air temperatures drop at night. It allows pool owners to extend their swimming season, often diving into the early days of winter, thanks to the consistent warmth provided by the solar pool cover.

Why Bubbles Facing Up is a Bad Idea for Solar Covers?

Installing a solar cover upside down with the bubbles facing skyward can significantly hinder its heating performance. Here’s a more detailed look at the issues caused by improper bubble orientation:

Compromised Daytime Heating

  • With bubbles facing up, the pool loses out on capturing optimal solar heat near the water’s surface.
  • The flat underside of the cover has limited direct contact with the water, meaning lower conduction efficiency.
  • The cover absorbs some warmth but lacks the heat-trapping capacity of thousands of bubbles.
  • Less heat is delivered to the pool during peak sunlight hours.

Nighttime Heat Loss

  • The thin underside touching the water doesn’t keep warmth effectively when temperatures drop at night.
  • Without the insulating effect of bubbles, more heat escapes into the cooler atmosphere.
  • Without bubbles facing down, the pool suffers from increased convection, conduction, and radiation losses.

Faster Cover Deterioration

  • The bubble side deteriorates faster when exposed to sunlight due to a lack of UV stabilization.
  • Underside rests on corrosive pool chemicals, which degrade the plastic on that side.
  • Trapped heat gathering in bubbles accelerates cover damage.
  • Bubbles start popping sooner as plastic sheets weaken.

Chlorine Odors Released

  • In direct contact with water, the underside takes in more chemical vapors, including chlorine.
  • As plastic heats up, absorbed chemicals are released into the air.
  • Users might experience more noticeable chlorine or other chemical smells

Limited Lifespan

  • Upside-down covers deteriorate faster from sun exposure and chemical damage.
  • Owners mistakenly think their cover was poorly made when improperly installed.
  • Instead of benefiting from the full potential lifespan of the cover, owners find themselves replacing it sooner than necessary.

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