These high airflow filters give your substrate and mycelium fresh air while maintaining high humidity levels. Manufactured with a strong 3M adhesive backing, these filters are made from 100% recycled filter material and sized to fit over 3" holes. Filters are slightly larger than monotub holes and are designed to keep out foreign spores and other contaminants. Use them in place of polyfill for time savings, fast application, and better protection against unwanted contamination.