Heidegger is interested to expand our sense of causality. He thinks that part of the problem with the world today is that we have limited ourselves to thinking about all that happens in the world only in terms of instrumental, mechanistic or machinic processes: inert thing x bangs into inert thing y, causing y to change (its place in the world if it moves, or its very nature, if the bang breaks it).
As always, Heidegger is makes use of Ancient Greek etymology. The word that gets translated into Latin as causis is aitia which has a broader meaning than just cause, something more like owing – as in, if y changes its place or nature as a result of x banging into it, it owes its new state to x. This is a very clever way to think about cause, because it still makes sense in the usual way we understand cause, but it adds a relational dimension to cause, a relationship between what does the causing and what gets caused (what suffers, or enjoys, being caused to change).
Having found this etymological link, between cause and something more like debt, Heidegger is keen to push the analogy further by arguing that that relation between what does the causing and what is caused is an ongoing one, and one that goes in two directions: not just from the causer to the caused, but from the caused back to the causer; if there is a debt owed to the causer, then the caused is responsible to the causer just as much as the causer is responsible for what happens to the caused. Responsibility of course implies discourse, conversing, responses back and forth.
So responsibility is a stage beyond debt, but an extension of it, one that enables Heidegger to begin to imagine a world in which the relations between things impacting on each other is not just inertly mechanical, but rather something more like an interpersonal conversation of care.
This should all be obvious to designers, who have been taught (if there education was worth anything) to pay close attention to materials; to recognize that their designs owe something to the quality of materials, what this or that material can and cannot do; instructors will often say to designers that their design is mistreating the material, not valuing it appropriately, not in conversation with a material’s wants and needs; all of which implies that the designer is responsible for being responsive to the material.
The opposite of being responsive/responsible to a material is violating it, challenging it to be what it inherently is not, or worse, not paying any heed to it at all, just treating it like a pile a stuff, and quantity (volume, weight) of anything.