WE CLAIM:
1. A fibrous material comprising fiber blends having plural types of solid fibers
having a common cross-sectional shape, wherein the composition ratio of each of at
least two out of the plural types of fibers to the total of the fiber blends is not less
than 5.0%, and when, among those plural types of fibers having a composition ratio
of not less than 5.0%, fibers having the highest and the lowest surface area increase
rates, which are given by the formula (1) below, are respectively designated as the
fiber(max) and the fiber(min), the surface area increase rate of the fiber(min) is reduced by
3.0% or more as compared to that of the fiber(max), and the composition ratios of the
fiber(max) and the fiber(min) to the total of the fiber blends are not less than 30.0% and
not less than 8.0%, respectively, and the fiber(max) has (a) a surface area increase rate
of not less than 1.20 and is (b) a porous fiber with a micropore specific surface area
of not less than 5 m2/g.
Surface area increase rate = (the circumference of a fiber cross section) / (the
circumference of a circle having the same cross-sectional area as the fiber cross
section) (1)
2. The fibrous material according to claim 1, wherein the micropore specific surface area of the fiber(max) is not less than 10 m2/g.
3. The fibrous material according to claim 1 or 2, wherein the fiber(min) is a porous fiber with a micropore specific surface area of not less than 5 m2/g.
4. The fibrous material according to claim 3, wherein the micropore specific surface area is not less than 10 m2/g.
5. The fibrous material according to any one of claims 1 to 4, wherein the occupancy rate Sfo against the circumscribed circle of the fiber(min), which is given by the formula (2) below, is not more than 0.90.
Occupancy rate Sfo against a circumscribed circle = Sf / So (2)
wherein Sf represents the cross-sectional area of a fiber cross section and So

represents the area of the circumscribed circle of the fiber cross section.
6. The fibrous material according to any one of claims 1 to 5, wherein the
modification degree Do/Di of the fiber(min) is not less than 1.10,
where Do represents the diameter of the circumscribed circle of a fiber cross section and Di represents the diameter of the inscribed circle of the fiber cross section.
7. The fibrous material according to any one of claims 1 to 6, wherein the surface area increase rate of the fiber(min) is not less than 1.10.
8. The fibrous material according to any one of claims 1 to 7, wherein the fiber cross-sectional shape of the fiber(min) is round or oval.
9. The fibrous material according to any one of claims 1 to 8, wherein the equivalent circle diameter of the fiber(max) is not less than 10 μm and not more than 1,000 μm.
10. The fibrous material according to any one of claims 1 to 9, wherein the Sfo ratio Z obtained by dividing the occupancy rate Sfo against the circumscribed circle of the fiber(min) by the occupancy rate Sfo against the circumscribed circle of the fiber(max) is not less than 0.20.
11. The fibrous material according to any one of claims 1 to 10, wherein the fiber diameter ratio Y obtained by dividing the equivalent circle diameter of the fiber(max) by the equivalent circle diameter of the fiber(min) is not more than 10.0.
12. The fibrous material according to any one of claims 1 to 11 which is composed of straight fibers.
13. The fibrous material according to any one of claims 1 to 12, wherein the fiber blend is composed of two types of fibers having a common cross-sectional shape.
14. The fibrous material according to any one of claims 1 to 13, wherein the ratio between the fiber(max) and the fiber(min) is from 10:1 to 1:2.
15. The fibrous material according to any one of claims 1 to 14, wherein the fiber(max) and the fiber(min) are produced from the same raw material.

16. The fibrous material according to claim 15, wherein the raw material is an ester group-containing polymer.
17. The fibrous material according to any one of claims 1 to 16 for use in medical applications.
18. The fibrous material according to any one of claims 1 to 17 for use in purification column applications.
19. The fibrous material according to any one of claims 1 to 18, which adsorbs β2-microglobulin with an adsorption capacity of not less than 0.005 mg/cm3.
20. A purification column comprising a plastic casing and the fibrous material according to any one of claims 1 to 19, in which the fibrous material is arranged in the plastic casing straight in the axial direction extending between openings on both sides of the casing, and an inlet port and an outlet port for a fluid that is to be treated are provided at either end of the plastic casing.
21. The purification column according to claim 20, wherein the equivalent diameter of flow cross-section is not less than 10 μm and not more than 250 μm.
22. The purification column according to claim 20 or 21, wherein the pressure loss achieved by allowing bovine blood to flow at a flow rate of 200 mL/min is from 0.5 to 30 kPa.