Is DE feminine or masculine in French?

When we use it as an indefinite article, "des" is used as the plural of both masculine and feminine:

masc.: "un garçon" > plural "des garçons"

fem.: "une fille" > plural "des filles"

When used as a contraction (from) "des" is either masculine or feminine. It is used as the plural form of both "de la" + feminine noun, and "du" + masculine noun.

masc.: "... du boudin" > plural "des boudins"

fem.: "... de la voiture" > plural "des voitures"

How they change:

fem.: de + la = de la

Before a noun starting with a vowel sound: de + l' = de l'

masc.: de + le = du

plural.: de + les = des.