De or het windvrij?

The correct Dutch article is:

de windvrij

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

How to use windvrij

the windvrijde windvrij
this windvrijdeze windvrij
that windvrijdie windvrij
our windvrijonze windvrij
your windvrijjouw windvrij
every windvrijelke windvrij
which windvrij?welke windvrij?
a big windvrij / the big windvrijeen grote windvrij, de grote windvrij