Adding some info that I got from talking to a vendor. The downside to exterior solar shades is that they can be 2x the cost of interior ones and the fabric choices are very limited. The other thing he mentioned is that if they are being used for blackout on a bedroom, for example, and are down on a windy night they might be loud. I was also told that interior shades, even if they are large, can be powerd by low voltage (wired), but exterior shades need to be on line votage.

We have been working on getting shades for some large, west facing windows in a newly acquired condominium. Interior shades are our only choice (and must be white facing out - so an aluminized solar shade would not work) and we've been told that the best interior shades for controlling heat transfer are an insulated honeycomb shade, vs. say a roller shade, or a lined roman shade, etc. Because of the weight of the honeycomb shades, we ran into an issue in automating the largest window (99" x 112") -- as it exceeds most manufacturers limits. I share this because you may want to check on what your automation options are if you have very large windows as that may inform your choice. Good Luck!

Thank you for the comment @rmsaustin. I am running into the same thing as well. Several windows are 96'x108', which already exceeds many manufacturers limits. We also have some 13' (156") wide windows. For those the vendor is suggesting using multiple shades.

I guess the other benefit of exterior shades is that they come in much larger sizes. I think the size limitations for interior shades has to do with the fact that they are usually either battery powered or low-voltage. With line voltage you can put in a much stronger motor.

Another benefit of exterior shades is cleaning (I think). With exterior shades it's probably enough just to hose them off once in a while (although they probably also get dirty much faster than interior ones).

Love my exterior Koolaroos! They stop heat before it enters the house, so yes, the company is right about not heating up the glass. Koolaroos were about 50 USD per 4' x 5' window so the price is right. There are many factors to consider for any window covering:

* Size (huge window? any solution will cost more)

* Accessibility (can you easily reach the window location to manually operate shades? if not, you may need motorized which sends cost skyward and often, reliability downward)

* Wind (outdoor shades always need anchoring, indoor ones may too, depending on whether you open the windows and what your typical winds and exposure are)

- Can wind anchoring hold shades in just full open or full closed, or can you have an intermediate position with anchoring? How do you operate anchoring?

* Appearance (very visible location where HOA demands perfection, or concealed sideyard where nobody cares?)

* How often will you need/want to adjust shade position? Multiple times daily? Or just when seasons change?

* Durability and resistance to UV, windblown soil (dirt/greasy pollen/air pollution/bird droppings/collected leaves etc.), water including standing or freezing water etc. etc.

- UV is very damaging to materials that aren't treated to resist it. Insist on UV-designed materials, otherwise your window coverings shred to bits in just a few seasons if your location is sunny

And above all, just think very hard about what your main goals and expectations are, throughout the day and with the change of seasons and weather. This can vary from window to window as each has a different exposure.

Just to agree with manufacturer - there is a huge difference between heat control on exterior and interior shades - as far as blocking solar gain.

Interior shades that are thick - like honeycomb style - will also block heat loss. They will also block heat gain but will warm the glass significantly and may void warranty. And they won't block the gain as well as exterior still.

So from an energy standpoint, it depends what you are trying to do - but it sounds like you are more concerned with blocking heat gain. Then exterior are much better.

Curious if you are doing both interior and exterior for the bedroom? I would think that exterior would not typically block all the light in most cases so then you would want interior coverings like curtains for true darkness.

I have a west window in the bedroom that has a film on the outside and curtain on the inside but am considering an exterior shade.

For the bedrooms I'm going with interior black-out shades only (and maybe sheer curtains for daytime privacy). Two bedrooms face north-east so I'm not worried about thermal issues. One faces south-west, but is under a very deep overhang so doesn't get any direct sun until after 5pm. There's only one that I'm not sure about since it's second floor, south-west facing and exposed, but it's more of a den/office. However, it would be nice if it could serve as a guest bedroom in a pinch. The solar shades I want to get are translucent since I don't want them completely blocking views when down. My contractor says for bedrooms they typically two two rollers - one translucent and one blackout (interior).

Another benefit of exterior solar shades that occured to me is prevention of bird strikes. I'm going to have very large windows and I'm worried about killing birds. I was going to talk to glass vendors about coatings. Maybe there is something that can work for both thermal and bird strike ?

Exterior shades and films will provide the best energy efficiency. Stopping the heat before it enters the home is always the best option. Exterior products never last as long and can run into all of the things mentioned above. Exterior window films have come a long way and now have 10-year warranties in a variety of options.

This is a mountain home with a 35% VLT exterior film installed which blocks about 65% of the incoming solar heat.

I love the versatility of interior vs. exterior solar shades!