1. A process for producing a multi-modal polyolefin, comprising: polymerizing the multi-modal polyolefin in the presence of a metallocene catalyst system in at least a slurry-phase polymerization stage and a gas-phase polymerization stage arranged in series in any order, wherein the multi-modal olefin comprises: (i) a first polyolefin fraction having a density of less than about 940 kg/m.sup.3, and (ii) a second polyolefin fraction having a density of less than about 930 kg/m.sup.3.

2. The process of claim 1 wherein the first polyolefin fraction has a density of less than about 930 kg/m.sup.3.

3. The process according to claim 1 wherein the second polyolefin fraction has a density of less than about 925 kg/m.sup.3.

4. The process according to claim 1 wherein the first polyolefin fraction has a melt index of 1 dg/min or greater, and wherein the second polyolefin fraction as a melt index of 3 dg/min or less.

5. The process according to claim 1 wherein the first polyolefin fraction has a melt index of 5 dg/min or greater.

6. The process according to claim 1 wherein the second polyolefin fraction as a melt index of 1 dg/min or less.

7. The process according to claim 1 wherein first polyolefin fraction is present from about 30% to about 50% by weight of the multi-modal polyolefin, and wherein the second polyolefin fraction is present from about 70% to about 50% by weight of the multi-modal polyolefin.

8. The process according to claim 1 wherein ethylene is present in the slurry-phase polymerization stage in an amount ranging from about 3 mol % to about 10 mol %, and wherein a co-monomer is present in the slurry-phase polymerization stage in an amount ranging from about 0.05 to about 0.6 mole of the co-monomer per mole of the ethylene.

9. The process according to claim 1 wherein the gas-phase polymerization stage has an ethylene partial pressure of about 6 bar to about 25 bar and wherein a co-monomer is present in the gas-phase polymerization stage in an amount ranging from about 0.03 to about 0.08 mole of the co-monomer per mole of the ethylene in the gas phase.

10. The process according to claim 1 wherein the multi-modal polyolefin comprises polyethylene.

11. The process according to claim 1 wherein at least ethylene and a co-monomer are polymerized to produce the multi-modal polyolefin.

12. The process according to claim 11 wherein the co-monomer used in the slurry reactor is 1-butene and the co-monomer used in the gas phase reactor is 1-hexene.

13. The process according to claim 11 wherein the co-monomer comprises from 3 to 12 carbon atoms.

14. The process according to claim 1 wherein the metallocene catalyst system comprises (C.sub.5H.sub.3Me,n-Bu).sub.2ZrCl.sub.2, where Me is methyl Bu is n-butyl.

15. The process according to claim 1 wherein the metallocene catalyst system comprises Me2Si(H4Ind)ZrCl2, where Me is methyl and H.sub.4Ind is tetrahydroindenyl.

16. The process according to claim 14 wherein the multi-modal polyolefin has a melt flow rate of about 0.1 dg/min to about 4.0 dg/min and a density of about 915 kg/m.sup.3 to about 924 kg/m.sup.3.

17. The process according to claim 15 wherein the multi-modal polyolefin has a melt flow rate of about 0.1 dg/min to about 4.0 dg/min and a density of about 915 kg/m3 to about 924 kg/m3.

18. The process according to claim 1 wherein the slurry-phase polymerization stage precedes the gas-phase polymerization stage.

19. The process according to claim 1 wherein the slurry-phase polymerization stage comprises a loop reactor.

20. The process according to claim 1 wherein hydrogen gas is introduced into slurry-phase polymerization and into the gas-phase polymerization stage.

21.-25. (canceled)
