De or het stressvrij?

The correct Dutch article is:

de stressvrij

Rule Words ending in -ij and -erij: usually de. See the rule

How to use stressvrij

the stressvrijde stressvrij
this stressvrijdeze stressvrij
that stressvrijdie stressvrij
our stressvrijonze stressvrij
your stressvrijjouw stressvrij
every stressvrijelke stressvrij
which stressvrij?welke stressvrij?
a big stressvrij / the big stressvrijeen grote stressvrij, de grote stressvrij