Gather your materials.
Place soap in glass cup and melt in microwave. Cook in 30 second intervals, lightly stirring in between, until smooth.
Finely chop thyme.
Mix in thyme and grapefruit zest until you get desired color and texture.
Coat soap mold with cooking spray and pour in your mixture. Let this stand for at least 1 hour and then place it in the freezer for 1 hour. Remove from mold and use within 3 months, enjoy!