Extended Surface Mini-Pleat Filters. Designed for high performance under both normal and difficult operating conditions, VariCel II and VariCel II with antimicrobial are appropriate for general HVAC and applications operating with variable air volume, turbulent airflow, and high humidity. The combination of durable construction and high efficiency also makes VariCel II ideal for specialized systems such as diffusion filters in paint booths and prefilters in cleanrooms.