Quantitative/Hardened Ashless Filter Papers. Made of 100% cotton linter cellulose, Ash Content: 0.01% (Except No.4A 0.025%), Acid washed: Double acid washed in hydrochloric then hydrofluoric acid (No. 3, 5A, 5B, 5C, 6, 7), then rinsed with ultrapure water to neutralize. No. 4A is