Fresh Wave Pets gel crystals don’t mask odor, they neutralize it without using toxic chemicals. Just open the jar to allow the gel crystals to absorb odors naturally. Place near kennels, kitty litter, habitats, pet beds, aquariums or anywhere continuous release action is needed to absorb stubborn pet odors. I put mine in my car and you’d never know I travel with two marsh-exploring Goldens. Lasts 30-90 days depending on ambient airflow. Replace when low. 16 oz.