car sunshades- background information

The problem

Modern cars with large windscreens, whether they have athermic glass or not, get very hot when parked in the sun during summer. And large rear windscreens compound the problem. Apart from the discomfort of stepping into an oven, or getting scorched by the seats, there is justifiable concern about toxic chemicals given off by outgassing of the the internal plastics when exposed to the sun. There is also the possibility of damage to the dashboard and interior fabrics.

The ultimate sunshade of course is a full car cover, and depending upon the material they are made from, can have a significant impact on cabin temperatures e.g.
http://www2.dupont.com/Tyvek/en_US/uses_apps/covers/tests_prove.html

However, for most people full car covers are not practical for everyday motoring. There are a number of companies that have addressed this issue with car-top covers for the windows only- most types you throw over, one deploys automatically! (see Links page). Like the full car covers it is preferable that your car is clean to avoid possible damage to paint work. Although offered in several sizes these covers are essentially generic. One company in the UK produces car-top covers for a specific sports car- the MGF/TF. These have the advantage that they also protect the fabric soft top from sun damage (and for this particular vehicle they might be useful when it rains as well!).

For windscreen covers, external reflective ones that cover the entire glass area would seem to be the most effective. Admittedly, they can be a pain to fit, particularly if it is windy, and having to hold the end in position against the door opening with one hand while closing the door with the other is not the best OH&S practice. It can also be a bit hazardous if you are trying to fit them in a busy narrow street. If the screen is not clean there is the possibility of fine scratches caused by the sunshade material fretting in the wind, and there is the possibility that they may be vandalised or missing when you return to your car. And because they are held in the door frame under the rubber seals, if it rains there is the possibility of water leaking into the car. This would not be that much of an issue unless the electrics for window opening etc were located on the inside of the door. I have seen one external sunshade on eBay that is tall enough for modern windscreens (96cm tall by 163cm wide) that  has a magnet enclosed in flap at the top middle, at a bargain price. Try searching for "Car Auto Magnetic Windshield Cover Windscreen Snow Ice Frost Protector".

Internal sunshades are the most popular type of sunshade on the market and come in a wide variety of types, sizes and materials.

The twist&fold wire-framed silver fabric ones are quite clever, and if they are a good fit for your car, are not a bad option. There are some unusual but somewhat intrusive sunshades that attach to the A-pillar and are drawn across the windscreen like a curtain, or others that repose on your dashboard and are raised like Roman blinds! Roll-up internal sunshades are common but the material often tends to remain rolled up, making it hard to fit, and they can be a pain to roll up inside the cabin. Which explains why concertina-type folding sunshades dominate the market.

The most common folding sunshades on the market are made from a reflective 'bubble wrap' material, which come either as plain reflective or adorned with artwork. If you can find one of these sunshades that fits your car, they are very cost-effective, although some of the artwork may leave residues on your windscreen and on some the fabric binding may eventually disintegrate into a fibrous mess. If they rely upon suction cups to keep them in place then the results are often disappointing, and on tall windscreens they often collapse in the middle.One advantage they do have is that they do not suffer from blistering (see below) and the gas trapped in the bubbles is air.

The other main type of folding sunshade is made from reflective 'foam-wrap', and at 5mm thickness is sufficiently rigid to span very tall windscreens. The gas used to manufacture the polyethylene foam is isobutane, a hydrocarbon commonly used in aerosol propellants and synthetic rubber. Before the foam is covered with aluminised PET it is good practice to allow the foam to outgas for at least three weeks, otherwise blisters may form under the impervious reflective layer. Outgassing increases at higher temperatures, and to help prevent any blisters forming on the outside of my sunshades I perforate the outer layer on a 1cm grid. So while the reflective (plastic) sunshades will keep cabin temperatures lower and may reduce outgassing from the car's interior, the shades themselves may produce a small amount of gas. As always, ventilating the car well after it has been closed is good practice, as is setting the air control to outside air, at least initially.

Model-specific sunshades

It seems puzzling that most motor manufacturers don’t offer sunshades as part of their accessory list. Admittedly, in markets like the US where there are many custom sunshade manufacturers, it might not be worthwhile for motor manufacturers to produce their own. The Americans have been making 'custom' sunshades for over two decades, and several companies make high-quality fold-up sunshades. The material they make them from is interesting and probably pre-dates the common reflective bubble-wrap/foam-wrap core material commonly available now. They attach cloth material to one side of a rigid 'board' and a reflective material to the other side. The individual panels are separated by stitching to allow them to fold up. They look good and are well made, but the rigidity probably explains the need for a cutout that is the full width of the rear view mirror, which tends to let in more light, particularly if the mirror is set low in the windscreen. If a dash mat is being used the cloth edge trim may catch on it while you are trying to fit the lower edge of the sunshade in place. The prices can be quite reasonable but it can be difficult to find a company that ships to Australia. However, there are now several services that provide a local intermediary postal address (e.g.  Australia Post Shopmate) in the US for companies that don't ship to Australia, so buying US sunshades may well be more feasible and less expensive than before. They ship using UPS rather than courier.  Note that the length of the parcels will be the height of  the windscreen which restricts the choice of postal services.
Several Australian car distributors now offer model-specific sunshades. Initially they were roll-up varieties, but they now have fold-up versions that are much more convenient to handle. They are almost certainly made in the US by a 'custom' sunshade manufacturer.

There are several manufacturers of quilted flexible sunshades. In Australia Solarscreen in QLD make sunshades mainly for the camper/motor-home market, and in the UK Silverscreens is a similar high-quality manufacturer. They are very well made and effective, and use high-quality suction cups to keep them in place. These sunshades are quite bulky when stored and there are divided opinions on suction cups. There are similar types of sunshades made in the US for trucks, although they are held in place by Velcro dotted around the edge of the window.

My fold-up front windscreen sunshades

I only started making sunshades because I could not buy any to fit our cars. After I had learnt how to make the necessary patterns I realised that I could probably make this a retirement hobby-business. The biggest challenge was to obtain suitable material that was sufficiently tall for modern windscreens. There was one brand of retail sunshade 90cm tall and made from 5mm thick polyethylene (PE) closed-cell foam core (basically foam-wrap) laminated with a reflective polymer (aluminised PET) layer on both sides. It was creased on alternate sides so that the panels fold up neatly. It was satisfactory for many of the smaller sizes but not for taller or very wide patterns.  I have now progressed to using Australian-made bulk rolls of this material 120cm wide and 6mm thick, that can be creased to suit the width of the individual patterns, to give full width panels across the entire width of the shade. Polyethylene foam has quite good insulating properties – at 50mm thick it has a R value of 1.5, typical of the level of insulation in many house walls. However, at 5mm thick it has a R value of only 0.18, not much more than 3mm thick window glass. Thus the effectiveness of the sunshade material is due almost entirely to the reflective layers.

Getting the sunshades past the rear view mirror nearly always requires a cutout - I make this as small as possible to maximise the efficiency of the sunshade. The sunshades are supported at the top by the sun visors without any need for suction cups. In instances in which the sun visors provide no support a magnetic attachment can be used. Mounts for GPS navigation devices etc. can be accommodated towards the bottom or side of the shade with the mounting position nominated by the owner. This would be the only time I would refer to them as 'custom' sunshades. A small additional cost is involved.

If a dash mat is to be also used I need to know about it, as it can affect the fit of the sunshade. Many cars have a groove at the base of the windscreen into which the sunshade sinks- a dash mat can block this, requiring a considerable reduction in the height of the sunshade.

These sunshades are sufficiently rigid to span the tallest windscreens found on modern cars including the Citroen C4 Picasso (113cm) and Peugeot 3008 (111cm).

In terms of longevity of the material we have used the same sunshades on our two cars since early 2009 here in Tasmania. Both have developed some blisters and after 5 years the one that has had the most exposure suffered splitting of the outer aluminised layer where the creases that project forward are stretched when the sunshade is folded.

Rear sunshades and fixed side windows

Rear sunshades present problems because while there is usually support from the parcel shelf at the bottom, there is no support at the top to hold them in place. Conventionally, suction cups would be used in this situation, but unless they are of very good quality they will often fail. Velcro dots could be used but generally the adhesive on the back of the dots is not as strong as the bond between the hooks and loops. This is aggravated by the often high temperatures to which they are exposed.

I have designed an alternative unobtrusive magnetic system. It requires 3-4 small magnets to be attached to the top of the glass inside with high-temperature 2-sided tape that I supply. Fitting the shade is simply a matter of placing the sunshade in position and it will snap into place. This system can also be adapted for rear windscreens that have no support at the bottom, and with fixed side windows. The strength of the magnets is sufficient to overcome the reduction in magnetic attraction at higher temperatures.

Sunshades for opening side windows

For doors that show exposed steel frames around the window glass, I can use magnetic attachments, but in this case the magnets are part of the sunshade. It simply needs to be placed in position and the hidden magnets will hold it against the door frame. The magnets are placed where the material tends to fold away from the glass, which means they work best on the particular side they have been designed for. My experience has been that the foam material shrinks slightly in length over time, so some magnets at the front and rear may not be in contct with the metallic frame. For window frames with non-metallic surrounds a press-in fit, using a slightly oversize pattern may work well. These can be used on either side, although the retaining strap will be visible from the outside on one side of the car. Feedback suggests that over time the material near the edge may permanently compress, making for a looser fit, but there have been no reports to date of them falling out. With no magnets they are significantly cheaper to make.


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