Our Picks to Help You Stay Cool and Save Money on Gas
Unless it’s cold outside, no one likes getting into a hot car. It can be hard to grab the steering wheel, make contact with the metal on your seat belt or sit on a leather seat. You may even start sweating after you get in the car. If you cannot park in the shade, what can you do to prevent this? Use a sunshade (AKA a “car sunshade” or “windshield cover”). A good sunshade will work. It will substantially reduce the interior temperature of your car and keep direct sunlight off various surfaces. There are other benefits to sunshades as well. If you have a cooler car when you get in (and follow our recommendations for cooling your car), you can substantially reduce your AC usage, which will improve your fuel economy and save you money at the gas pump. Sunshades are a bargain. You get all these benefits for less than $15 and a good one will last for years. Everyone should have one in their car.
What did we do?
We identified leading sunshades at reasonable price points and then evaluated them for quality and ease of use. We then consulted with our Scientific Advisory Board to devise and implement a real-world test to assess the cooling power of the highest quality and easiest to use sunshades.
What did we learn?
- Using sunshades or a reflective car cover when parking reduces temperatures inside your car (even when it’s cloudy), meaning you are more comfortable and your AC doesn’t have to work as hard to cool you down when you get back in, which also saves you gas.
- Sunshades cool down surfaces in the front cabin of the car (dashboard, front seat) especially well – as much as 51.1 degrees (F) in our trials.
- Of the three sunshade designs we tested, the “bubble” shade was more effective at reducing in-car temperatures than both the “twist-and-fold” and “two-piece” shades.
- Side window sunshades add to the comfort of the backseat occupants but do not contribute significantly to cooling. However, these shades can impair side visibility.
- Reflective car covers provided the highest amount of cooling (the one we tested reduced the interior temperature 5-10 degrees (F) compared to sunshades) but are more expensive and cumbersome to use.
- Although the pros outweighed the cons on our recommended shades, we believe that each design has flaws, and that better design could improve utilization of each type of shade.
What did we like?
- The “bubble” shade: an accordion style shade with fluid filled bubbles (Motor Trend Accordion)
- Over the side window mesh sunshade (TFY)
- Solar/Reflective car cover (AUDEW)
How did we figure this out?
No one enjoys stepping into a hot car, especially because you’ve usually walked across a hot parking lot on a hot day to get there. Not only are they unpleasant, but there are some hidden costs associated with operating hot wheels. The hotter your car, the harder your AC and your engine must work to cool the interior down – translating to more emissions and money at the pump. One Oak Ridge National Lab study found that using your AC while idling increases your fuel use by 55-60% and by 9-14% at highway speeds.
Sunshades purportedly lower the interior temperature of your car, making you more comfortable and reducing some of that aforementioned strain on your AC. Do sunshades work? If so, how much do sunshades actually help cool a car? We set out to quantify temperature reductions and then use our results to inform which designs were best. We purchased 15 different sunshades for our test. We eliminated some literally right out of the box because they tore when first opened/used or were virtually impossible to twist/fold back into a manageable shape and size. After more ease of use testing, we picked six finalists for actual in-car testing.
- The “twist-and-fold” shade: an expandable fabric one-piece shade that folds (with considerable effort) into a pouch when not in use (Ohuhu).
- The “bubble” shade: an accordion style shade with fluid filled bubbles (Motor Trend Accordion).
- The “two-piece” shade: similar to the “twist-and-fold” shade, but comes in two separate pieces for greater adaptability and coverage (Custom Accessories).
In addition, we also tested side window shades as well as reflective car covers to better understand whether these provided additional cooling effects.
- Over the side window mesh sunshade (TFY)
- Twist with suction cup side window sunshade (Kalmore)
- Solar/Reflective car cover (AUDEW)
To control for environmental factors, we parked two nearly identical cars next to each other. One blue 2008 Honda Fit was parked without a sunshade, while another blue 2017 Honda Fit was parked with a sunshade. We chose a flat and open lot, and parked the cars facing south to maximize incoming solar radiation. To minimize variation, we chose a location away from shading structures, including trees, buildings and other cars. We conducted the test over four summer days in Santa Barbara, CA between the hours of 12pm to 2:20pm, doing our best to find days with similar weather. Each day was dedicated to testing one of the sunshade designs. To ensure the two cars didn’t heat up unequally, we had the cars arrive at the chosen location at nearly the same time (20 minutes before the test), and kept the windows down and doors open until the test began.
Using a serious thermometer and thermocouples, we measured and recorded interior temperature every 15 minutes in four different locations: (1) the dashboard, (2) the front seat, (3) cabin air temperature at chest level and (4) cabin air temperature at head level. By comparing the two cars, we were able to obtain a complete picture of how much the car was being cooled by the sunshade over time. After the data from the first three days were analyzed, we expanded upon the test by adding side window shades to the best performing sunshade to analyze whether they have an impact on cooling.
For the reflective car cover test, we obtained a 2008 Toyota Highlander as our test vehicle due to the fact that the smaller car covers were out of stock. We ran a three-day test: On day 1, we obtained head-level cabin temperatures as a control; on day 2, we obtained temperature readings with a sunshade only; and on day 3, we measured interior temperatures with the car cover. Test conditions were similar for all three days, with slight variation in temperature and 25% cloud cover on day 3 for the first 30 minutes.
In general, in our control cars, car temperatures increased rapidly within the first half hour, maxed out between hours 0.5 and 1.5, and then plateaued slightly below maximum temperatures. Surface temperatures of the dashboard and front seat were much higher in the control car than in the car with a sunshade. The maximum temperature reached during testing was a blistering dashboard reading of 184.6 degrees (F) in the control car during day 2 bubble shade testing.
Figure 1: A sample of temperature data through time of dashboard temperatures for the control car (no shade, blue) and the test car (bubble shade, orange).
However, less of a difference, and even negative changes in temperatures were observed when measuring chest-level and head-level cabin air temperatures. One possible explanation for this is that air is heating up and reaching a maximum temperature or escaping.
Figure 2: A sample of temperature data through time of head-level cabin air temperatures for the control car (no shade, blue) and the test car (bubble shade, orange).
Though surprising, air temperature is less important than the surface temperatures of your car. Air will escape rapidly out of your car once the windows are open or the AC is turned on, while surfaces will continue radiating heat long after you turn on the car.
Weather conditions also varied slightly between each day. When testing the twist-and-fold shade on day 1, it was partly cloudy from 12-1pm and sunny for the remaining 1.5 hours, with temperatures ranging from 69-75 degrees (F). Bubble shade testing took place on a sunny day 2, with temperatures ranging from 72-77 degrees (F) and no cloud cover. Day 3 testing of the two-piece shade also had no cloud cover, but was windy with temperatures ranging from 75-78 degrees (F). Day 4 was sunny with a slight breeze – temperatures ranging from 75-81 degrees (F).
The bubble sunshade performed best, resulting in the highest temperature reductions. The second-best performer was the two-piece shade, while the third-best performer was the twist-and-fold shade. Some of this was likely due to the weather: day 2 (bubble shade) was hot and not windy, day 3 (two-piece) was hot but windy, while day 1 (twist-and-fold) was the least hot and slightly cloudy. That said, the natural variations in ambient temperature were not drastic between days, and these conditions likely explain only some of the difference in the observed effect of each design.
Figure 3: Maximum temperature reductions observed from using a sunshade at each location, for three sunshade designs: twist-and-fold, bubble and two-piece.
Table 1: Maximum and median reductions in temperature between a control car (no sunshade) and test car (with sunshade) over a 2.5 hour period, from 12:00-2:30pm. Table displays all 3 tested designs. Measurements were taken in 15 minute increments.
|Temperature Reduction (°F)|
|Dashboard||Front Chair||Air (Chest-Level)||Air (Head-Level)|
|Twist & Fold:|
Overall, all three sunshade designs demonstrated significant temperature reduction potential over a control car with no sunshade. While this is certainly true, we noticed some potential issues as well. The accordion shade was the easiest to fold but does not fit all cars (and had to be propped up during testing). The twist-and-fold shade in theory took up less storage space than the bubble shade, but was difficult to fold up and stow away, even after we became experienced with them. The two-piece shade offered better coverage than the twist-and-fold shade, but was perhaps even more difficult to fold and store.
TFY Side Window Shade
With the bubble shade being the best performer, we then expanded upon this with the addition of the side window shades on day 4 testing.
Figure 4: A sample of temperature data through time of head-level cabin air temperatures for the control car (no shade, blue), the test car (bubble shade, orange) and the test car (bubble shade with side window shades, grey).
From our test, we cannot determine whether the side window shades had significant cooling effect. Some variables that may have impacted this test include the fact that we had to change the test vehicle to a full-size SUV as our original test vehicle was no longer available for use. Also, day 4 of testing with the side shades was also hotter compared with the control and bubble only test days.
Overall, our testers found that they enjoyed the side shades as they cooled the occupants and allowed them to have their windows open while the car is moving. The product was very easy to don and doff – as a bonus, we were able to easily and quickly stuff it back into the provided bag. However, there are a few quirks with this product – with both side window shades up, it can impair your ability to check your blind spots. Therefore, we recommend having your backseat passenger sit in the passenger side to reduce the impairment. Our testers also observed that at higher speeds, some flapping and noises are evident – but they were fixed by rolling the windows up 1/3 of the way.
Twist Style Shade
This shade did not provide any additional cooling effect as it only covered 75% of the window. Occupants did mention that the seat was less hot when the car was parked and it was less obstructive to the driver compared to the TFY shades. However, it does not allow for the side windows to be rolled down nor does it fit easily back into the bag for storage.
Reflective Car Cover
Our data showed that the reflective car cover has the highest amount of cooling power. Where the sunshade was able to reduce the cabin temperature over 4 degrees (F), the car cover reduced our temperature by almost 10 degrees (F).
Figure 5: A sample of temperature data through time of head-level cabin air temperatures for the control car (no shade, blue), the test car (bubble shade, orange) and the test car (car cover, grey).
Our testers reported that the cover was easy to put on our test vehicle – it has side mirror pockets to help differentiate front and rear. In addition, there are straps at the front and back to secure the cover to the car, ensuring that the wind will not carry it away. It appears to be well made and the reflectiveness of the cover is not blinding (thankfully). Some downsides of it include storage and the price. Unfortunately, it does not easily fit back into the bag provided (like most sunshades, which are virtually impossible to stuff back into their carry bags) and the cover costs $40. Therefore, we would recommend this product to people who must park their vehicle in the sun (and drive it after it has solar-warmed) several times a week or must leave it in the sun for extended periods between drives.
Though the products are not without their flaws, it is clear after testing that they are a worthwhile investment. In addition to making you more comfortable, they can save you money and shave off unnecessary emissions by reducing AC use (which substantially reduces fuel economy at idling and low speeds). While you likely won’t be saving hundreds of dollars annually with a sunshade, you will be saving some money every year: We estimate about $27/year in gas savings (through reduced AC use) for someone who parks in the sun 180 times/year, doesn’t use a sunshade, and runs their AC to cool their car for at least 10 minutes. At less than $15 for most models and a long life-span, it’s hard to go wrong buying a decent sunshade.
Based on these findings, we recommend always using a sunshade. While there are some designs that are better than others (we liked the bubble shade the best), all three sunshade designs significantly reduced interior car temperatures. Always using a sunshade is a great practice to increase your comfort when you drive while helping you to save money and the planet. As for the rear window shades, children and pets that typically sit in the backseats will appreciate the shade provided – especially after a hot day in the sun. Finally, those that do not use their vehicles daily will greatly benefit from a reflective car cover in protecting the exterior and interior of their car.