TECHNOLOGY FOCUS - POLYMERS - Preferred film: A film comprising the polymer composition has water vapor permeability of 0.40 g/m2.day or less, and haze value of 20% or less at thickness of 100 mu m. EXAMPLE - 1-hexene (in weight parts) (0.55), diisopropyl ether (0.30), triiso butyl aluminum (0.20) and isobutyl alcohol (0.075) were mixed with cyclohexane (500) and spin-dried in nitrogen atmosphere. Then, tungsten-hexachloride toluene solution (15) and bicyclo(2,2,1)hept-2-ene (250) were added and polymerized at 55 degrees C, to obtain polymer (I) having weight average molecular weight of 83000 and molecular weight distribution of 1.8. T8400 (RTM: diatomaceous earth supported nickel catalyst) (0.5) was added to polymer (I) and reacted at 160 degrees C under hydrogen pressure of 4.5 MPa for 6 hours, to obtain solution. The solution was filtered, added into isopropyl alcohol (3000), hydrogenated substance was precipitated, filter was separated, recovered, washed with acetone (500) and dried at 100 degrees C for 48 hours, to obtain ring-opened polymer hydrogenated substance (A) (190). A mixture (7) containing tricyclo(4.3.0.12,5)deca-3-ene and tetracyclo(4.4.0.12,5.17,10)dodeca-3-ene and cyclohexane (1600), diisopropyl ether (0.84), tri-i-butyl aluminum (0.55), isobutyl alcohol (0.21), 1-hexene (3.94), and solution (24.1) containing tungsten-hexachloride dissolved in cyclohexane were mixed and stirred at 55 degrees C for 10 minutes. Subsequently, tungsten-hexachloride solution (48.9) containing norbornene and dicyclopentadiene, tetracyclo dodecane dissolved in cyclohexane was added and polymerized for 30 minutes, to obtain ring-opened polymer (B) having weight average molecular weight of 20000 and molecular weight distribution of 1.9. Ring-opened polymer hydrogenated substance (A) (90) and ring-opened polymer (B) (10) were mixed and extruded, to obtain pellet of polymer composition. The obtained pellet of polymer composition was molded, to obtain single layer film. The obtained single layer film had thickness of 101 mu m, water vapor permeability of 0.38 g/m2.day or less and haze of 19%.