Humidifier Wick Filter Extra Long-Life Replaces Holmes WF2 Kaz ReliOn HW500 HAC-504 HCM350 =REUSABLE= Made of Dura-ester, a durable synthetic polymer, Not Paper. Can be washed and rinsed to remove dust and calcification The filter lasts longer than paper filters. Pays for itself quickly! Visit www.mynaturalbreeze.com for more info! Compare to Honeywell Part # HAC-504AW. Dimensions: 5 H x 4 1/4 ID x 6 1/2 OD x 1 Thick.