Claims

1.

A flexible envelope for sealing a duct, the envelope having an outer surface defined by two sheet portions that overlie each other and that are secured to each other at a plurality of locations internally of the envelope to define a plurality of inflatable chambers in communication with each other, sealing means being provided on the outer surface to seal the envelope to the duct.

2.	An envelope according to claim 1, wherein the securement of the sheet portions to each other is effected by welding the sheet portions together.

3.	An envelope according to claim 1, wherein the securement of the sheet portions to each other is effected by bonding, preferably by the formation of adhesive bonds.

4.	An envelope according to any of the preceding claims, wherein the securement locations extend along at least one substantially straight line.

5.	An envelope according to claim 4, wherein the securement locations extend discretely along said at least one line.

6.	An envelope according to any one of the preceding claims, wherein the two sheet portions are formed from separate sheets that are sealed together peripherally.

7.	An envelope according to any one of claims 1 to 5, wherein the two sheet portions are formed from a single sheet that is folded over and sealed peripherally.

8.	An envelope according to any one of claims 1 to 5, wherein the two sheet portions are formed from a single tubular member.

9.	An envelope according to any one of the preceding claims, wherein each sheet portion is of laminate construction.

10.	An envelope according to claim 9, wherein the laminate comprises metallised polymeric material.

11.	An envelope according to any one of the preceding claims, of generally rectangular configuration.

12.	An envelope according to any one of the preceding claims, wherein the sealing means comprises a layer of mastic or adhesive.

13.	An envelope according to any one of the preceding claims, wherein the sealing means comprises elastic material.

14.	A duct sealed by an inflated envelope in accordance with any one of the preceding claims being inserted therein.

15.	A duct according to claim 14 having at least one elongate member extending therefrom, and wherein the envelope seals the or each elongate member into the duct, and the sealing means seals the envelope to the or each elongate member.

16.	A duct according to claim 14 or 15, wherein the envelope is wrapped over onto itself with the inflated chambers thereof interlocking thereby to resist movement of the envelope along the duct.

17.	A method of sealing a duct, wherein an envelope according to any one of claims 1 to 13 is inserted into the duct and inflated into sealing contact therewith.

18.	A method according to claim 17, wherein the duct has at least one elongate member extending therefrom and the envelope is positioned to seal the or each member within the duct.

19.	A method according to claim 17 or 18, wherein the envelope is wrapped around onto itself.