You pay attention to every item that goes into your backpack if you're going to carry it for 330 miles (about 530 kilometers).
That was my state of mind when I planned a walk around the north of England with my partner.
I scrutinized every item. Does it provide sufficient value? Can I find something equivalent but lighter?
I used a spreadsheet to maintain a running total of the weight of our packs. Eventually each pack would weigh 14 lb (about 6.4 kilograms).
Our spectacle cases at 3 to 4 ounces (around 100 grams) each were preventing me from reaching the 14 lb goal. Our three cases would be approaching 3% of our total load. Not a lot, but I was getting compulsive about that goal.
I couldn't find spectacle cases that were sufficiently lightweight and crushproof. Then I learned from a Web discussion group about tenite butyrate tubing.
I ordered tubing and caps from US Plastics. I cut the tubing with a boxcutter.
A case for three spectacles is about 2 ounces (about 54 grams). That's close to half the weight of just one hard-sided case.