Think about it, instead of having a straight tube ink refill, how about fashioning it as a spiral? Agreed it occupies a bit more space so the pen can’t be sleek and slim, but it holds double the amount of ink! There’s a reason why our DNA is structured in a double helix. I guess it will work like a charm for those disposable types, making them last longer. I won’t call this project 100% eco-esque but it’s a step towards it!