This is one of those small things that matter from a packing efficiency perspective. It is actually a very silly, common sense little topic but where market trends may easily lead us to the dark side.
It bears mention and stress: this is about long distance backpacking where “long” is more a factor of a day vs. multi-day rather than thousands of miles at a time. Once you’re out for an overnight, you fall into the long distance realm as far as packing goes. The gear you will need for an overnight or a few days out won’t differ much from what you may need for a multi-month trip. Such gear defines a packing style where volume and weight matter. A lot.
This one’s about volume.
The case for compact sunglasses
Sunglasses are one of those items that are important, bordering the essential in most trips. Eyes do suffer in high light environments and recurrent exposure may lead to long term eye issues. At the same time, sunglasses may be packed away plenty of the time. How much it really depends on the individual, some people like to wear them even if not strictly needed, some carry them on their heads when not in use.
Sooner or later, sunglasses will be packed. Then you’ll welcome this two features:
Both are related. They actually go together. A compact bundle will not only take less volume, it’ll also offer less chance of breaking in an item that’s inherently fragile.
Sunglasses for serious outdoor use must offer wrap-around cover so excess lighting doesn’t get in from the sides. Most current glasses implement this feature with a wrap-around frame and lense, 90s Bono style. This makes the folded glasses 3 dimensional. Like this:
This structure takes a lot of volume when folded and it must support 3 dimensional stress, which it’s not ready to take. Packing this thing takes not only volume, it also takes care.
A 2 dimensional design is better in all those accounts. Side protection may be implemented by soft fabric. It works the same as far as protection goes and it’s not part of the structure of the glasses. Like this:
This model folds down to 2 dimensions, all elements in parallel planes. It takes far less volume, the frame and lenses are less vulnerable and it offers a slim profile to side stress. This glasses are strong enough to not need a hard case. I commonly use a ziplock to protect them from scratches and dirt.
The difference is best seen with both models together:
The fabric sided model will offer a narrower angle of vision, you need to turn your head to compensate. I personally welcome the compromise.
The other issue you will find with this engineering wonder is at the time of purchase. Most of the target sunglasses you’ll find will be of the folded 3 dimensional flavor. You’ll need to shop around, dig deep on the relevant aisle and still you won’t have much to choose from. No fancy colors.
The market bias towards the wrapping frames is probably more about fashion than function but it shows a common issue with gear: backpacking remains a small, commercially unattractive niche whose specific needs are often not considered at the time of design.
Whatever you find, make sure the fabric sides are removable if you mean to take this glasses to the disco in town stops.