>And a less obvious application is in an easy-to-clean filter: stretch this filter and its pores grow, allowing stuff stuck in them to be flushed through when the filter is washed.
That doesn't make sense to me. If the auxetic threads making up the filter expand, then the negative space between them will shrink, so you'll get smaller pores, not larger ones.
The threads themselves don't expand, its that they re-arrange themselves so the material is larger in total volume, but the voids within the material are also larger. The solid material itself, of course, must be conserved. Think of a sponge: normally if you stretch it the pores get smaller. Auxetic materials can be engineered so the pores get larger, but the amount of sponge stays the same.