the sealing layer of the film according to the present invention comprises a polymer selected from the group consisting of polyethylene and ethylene - α - olefin copolymers with a density ≧ 0 . 915 g / cm 3 . preferably said sealing layer will comprise at least one ethylene - α - olefin copolymer with a density ≧ 0 . 915 g / cm 3 . preferred polymers are those , either heterogeneous or homogeneous , with a density comprised between about 0 . 915 and about 0 . 935 g / cm 3 , and even more preferred those with a density of from about 0 . 917 to about 0 . 930 g / cm 3 . the melt flow index of said polymers to be used in the construction of the sealing layer in the film according to the present invention generally ranges from between about 0 . 1 to about 5 g / 10 ′ and preferably between from about 0 . 5 to about 2 . 5 g / 10 ′. melt flow index ( mfi ) is measured according to astm d1238 condition e ( 2 . 16 kg loading at 190 ° c .). in general these polymers may be blended with one or more other polymers compatible therewith , such as polyolefin polymers . these blends will typically comprise 50 % or more , preferably 70 % or more and even more preferably 80 % or more by weight of polyethylene and / or ethylene - α - olefin copolymer with a density ≧ 0 . 915 g / cm 3 . in a preferred embodiment of the present invention , said sealing layer will essentially consist of polyethylene and / or ethylene - α - olefin copolymer with a density ≧ 0 . 915 g / cm 3 . in another preferred embodiment said sealing layer will essentially consist of a blend of at least 80 % by weight of polyethylene and / or ethylene - α - olefin copolymer with a density ≧ 0 . 915 g / cm 3 with up to 20 % by weight of one or more polymers selected from the group consisting of ethylene - vinyl acetate copolymers , ethylene - alkyl acrylate copolymers , anhydride grafted ethylene - alkyl acrylate copolymers , ethylene - alkyl methacrylate copolymers , anhydride grafted ethylene - alkyl methacrylate copolymers , ethylene - acrylic acid copolymers , ethylene - methacrylic acid copolymers , and ethylene - maleic anhydride - alkyl ( meth ) acrylate terpolymers . the sealing layer will typically be at least 4 μm thick , preferably at least 7 μm thick , and even more preferably at least 9 μm thick . generally the thickness of said sealing layer may range from about 4 to about 25 μm , depending on the overall film thickness and on the number of layers in the structure . films according to the present invention are preferably multi - layer films comprising besides the sealing layer as described above at least one core gas - barrier , layer and one outer abuse layer . the gas of main concern is oxygen and transmission is considered to be sufficiently low , i . e . the gas - barrier material is relatively gas impermeable when the transmission rate is below 100 cm 3 / day . m 2 . atm as measured according to the procedures of astm d3985 at 23 ° c . and 100 % relative humidity . to obtain oxygen barrier layers with a transmission rate below that value , pvdc or evoh , possibly blended with a polyamide or copolyamide , can advantageously be employed . preferably however the barrier layer will comprise evoh as this polymer can be irradiated even at high dosage levels without degradation . with an oxygen barrier layer comprising evoh an irradiated fully coextruded structure is typically employed what reduces any possible risk of delamination that might be present in case of extrusion coated structures when they are subjected to a drastic heat - treatment . once the gas - barrier resin has been selected , its thickness will be set to provide for an oxygen transmission rate below 100 cm 3 / day . m 2 . atm . typically the thickness of the barrier layer ranges from about 2 to about 10 μm , preferably from about 3 to about 8 μm , and more preferably from about 4 to about 7 μm . as the outer abuse layer , particularly when an ethylene - vinyl alcohol copolymer is used as the barrier layer , a moisture - barrier material , such as an ethylene homo - or co - polymer or a propylene homo - or co - polymer is preferably employed . as an example said outer abuse layer may comprise a polyethylene , an ethylene - α - olefin copolymer , an ethylene - vinyl acetate copolymer , an ionomer , a blend thereof with modified polyolefins , a polypropylene , a propylene - ethylene copolymer , etc .. according to a preferred embodiment of the invention said outer abuse layer will comprise an ethylene - vinyl acetate copolymer . in a most preferred embodiment said outer abuse layer will comprise an ethylene - vinyl acetate copolymer with a vinyl acetate content of from about 4 to about 14 % by weight and more preferably of from about 5 to about 9 % by weight , preferably with a melt flow index lower than 1 g / 10 ′, optionally blended with a heterogeneous or homogeneous ethylene - α - olefin copolymer with a density of from about 0 . 900 to about 0 . 935 g / cc . the thickness of said outer layer is not critical and it is generally comprised between about 2 and about 35 μm , preferably between about 6 and about 30 μm and more preferably between about 10 and about 25 μm . additional layers , such as for instance tie layers to improve interlayer adhesion , or bulky structural layers to provide the overall structure with the desired mechanical properties , or shrink layers to improve the shrink properties of the heat - shrinkable films , can be present as known in the art . if the structure contains tie layers their thickness is generally comprised between about 0 . 5 and about 7 μm , and preferably between about 2 and about 5 μm . non limitative examples of suitable , preferred , structures are for instance 5 -, 6 - or 7 - ply structures of the following type : wherein the inner structural layer , that may be equal or different from the outer abuse layer , may comprise one or more polymers selected from the groups of polyolefins , polyamides and copolyamides . preferably the film according to the present invention is a heat - shrinkable film . irradiation may be accomplished by the use of high energy electrons . preferably electron radiation up to about 200 kgy dosage level is employed . the irradiation source can be any electron beam generator operating in a range of about 150 kv to about 6 mv with a power output capable of supplying the desired dosage . many apparatuses for irradiating films are known to those skilled in the art . irradiation is usually carried out at a dosage of from about 50 to about 160 kgy , preferably at a dosage of from about 60 to about 150 kgy , and more preferably at a dosage level of from about 70 to about 140 kgy . irradiation can be carried out conveniently at room temperature , although higher and lower temperatures , for example 0 ° c . to 60 ° c ., may be employed . in case of heat - shrinkable films , as indicated above irradiation is preferably carried out on the primary tape before orientation as irradiation has the main purpose of improving bubble stability . if this is not necessary however , irradiation , to improve the structure strength , can be carried out also after orientation . the films according to the present invention can be prepared by conventional method of manufacturing , by extrusion , coextrusion or extrusion coating through a round or flat die , followed by irradiation . preferably however , as indicated above , the film is manufactured by coextrusion . when , according to a highly preferred embodiment of the invention , a heat - shrinkable film is desired , the primary tape thus obtained is quenched and oriented , either by tenterframe , in case of extrusion through a flat die or by a tubular orientation process in case of extrusion through a round die . irradiation is preferably carried out before orientation , but in some cases it can alternatively be carried out after orientation . the corona treatment of the sealing layer is carried out just before conversion of the film sheet or tubing into containers by impulse - sealing the film to itself . it is performed in the conventional manner . when the film is in the form of a seamless tubing , corona treatment of the innermost layer is carried out by inflating the tubing with a gas , such as air or other gases such as nitrogen , carbon dioxide , oxygen , ozone , etc ., and the mixtures thereof as known in the art , in an amount sufficient to prevent the contact of the internal surfaces of the tube while keeping the tubing in a substantially flat state , and the corona discharge treatment of the innermost sealing layer is conducted from the outside by positioning at least one discharge electrode and at least one counter electrode closed to the upper and lower outer surfaces of the inflated tubing , suitably adjusting the distance between the electrodes to contact the outer surfaces of the inflated tubing , and discharging electricity from the discharge electrode to the counter electrode through the inflated tubing . the optimum corona treatment level will depend on the kind , thickness and feed rate of the film to be corona treated . it has been found that the improvement in sealability is obtained when the conditions for corona discharge treatment are adjusted so that the treatment provides the surface of the sealing layer with a wet tension strength of at least 30 dyne / cm , preferably at least about 35 dyne / cm , more preferably at least 40 dyne / cm . the corona treatment energy level generally employed with the film according to the present invention is typically from about 150 to about 500 ma . however , lower or higher energy levels might also be suitably employed to provide the film surface with the desired wet tension strength . the obtained tubing is then converted into bags by cutting lengths of the tubular film and sealing such lengths transversely to obtain end - seal or bottom seal bags . alternatively the tubing is cut and sealed in such a way to obtain side seal bags . the bags obtained from the film according to the present invention show outstanding properties in terms of cold and hot seal strength . thus when such bags are used in food packaging , the food item is inserted in the bag , the package is vacuumized and closed by heat - sealing or by clipping , and the package can then be subjected to various heat treatments such as cooking at a temperature up to about 85 ° c . for several hours or pasteurisation treatment at 95 ° c . for 1 hour . the bags stand these treatments without revealing damages or weakening of the seal . the examples which follow , only purport to illustrate the invention and not to restrict its field of application . the following abbreviations have been used in the following examples to identify the materials : pe1 heterogeneous ethylene - α - olefin copolymer with d = 0 . 920 g / cm 3 and mi = 0 . 8 - 1 . 2 g / 10 ′ ( dowlex ™ 2044e by dow chemical co .) pe2 homogeneous ethylene - α - olefin copolymer with d = 0 . 923 g / cm 3 and mi = 0 . 85 g / 10 ′ ( affinity ™ xu59900 . 00 by dow chemical co ) pe3 heterogeneous ethylene - α - olefin copolymer with d = 0 . 920 g / cm 3 and mi = 4 . 4 g / 10 ′ ( stamylex ™ 1046f by dsm ) pe4 homogenous ethylene - α - olefin copolymer with d = 0 . 918 g / cm 3 and mi = 3 g / 10 ′ ( affinity ™ dsl 1515 . 00 by dow chemical co .) pec heterogeneous ethylene - α - olefin copolymer with d = 0 . 911 g / cm 3 and mi = 5 . 7 - 7 . 5 g / 10 ′ ( stamylex ™ 08 - 076 f by dsm ) lg1 anhydride modified eva - based adhesive with mi = 0 . 9 - 1 . 3 g / 10 ′—( bynel ™ 3062 by dupont ). eva1 eva ( 6 % va ) with mi = 2 . 5 g / 10 ′—( escorene ™ fl 00206 by exxon ). eva2 eva ( 13 % va ) with mi = 2 . 5 g / 10 ′—( escorene ™ fl 00212 by exxon ) eva3 eva ( 13 % va ) with mi = 0 . 4 g / 10 ′—( evatane ™ 1003 vn 4 by elf atochem ) eba ethylene - butyl acrylate copolymer ( 7 % ba ) with mi = 1 . 1 g / 10 ′ ( ncpe - 6472 by borealis ) emaa ethylene - methacrylic acid copolymer ( 12 % maa ) with mi = 1 . 4 - 2 . 0 g / 10 ′ ( nucrel ™ 1202 by dupont ) evoh ethylene - vinyl alcohol copolymer with 44 % by mole of ethylene content and mi = 4 . 9 - 6 . 1 g / 10 ′—( eval ™ ep - e105a by marubeni ) 6layer films of general structure a / b / c / d / c / e , wherein the resins employed for the different layers are as indicated in following table i , are prepared by coextrusion from a round die , followed by a quick quenching with cold water , irradiation to the dosage level indicated in table i , heating with hot water ( 96 ° c .) and biaxial orientation at this temperature with stretching ratios of 2 . 8 × 3 . 4 ( md × td ). the thickness of the end film was 60 μm , and the ratio between the layers was 3 / 3 / 1 / 1 / 1 / 5 . the sealing layers of the obtained tubing were then corona treated at 240 ma . the films of comparative examples ( ce ) 1 to 9 were obtained by following exactly the same procedure as in examples 1 to 9 but avoiding the corona treatment . the tubular films of examples 1 to 9 and of comparative examples 1 to 9 have been converted into 300 × 500 mm end seal bags by a continuous process . the bag - making machine was run at 120 bags / minute and the impulse of the sealing wire was set at 14 . 5 a . cold and hot seal strength of the obtained bags have been evaluated by the methods indicated hereinbelow in line and in some cases also after 3 - week ageing . the cold seal strength has been evaluated by the test of the parallel plates ( pp ) that provides for a bag to be confined between two plates a specified distance apart and be inflated until the seal fails . the pressure level inside the bag at the point of failure is a measure of the quality of the seal . the results of this test are reported in inches of water pressure ( iowp ). the hot seal strength has been evaluated by the test of the variable pressure hot burst ( vphb ) that provides that a clean sealed bag be inflated to a specified dwell pressure and the seal area be submerged in hot water at 85 ° c . after ten seconds the pressure inside the bag is increased at a specified rate ranging from 1 to 7 inches of water / second ( 2 . 49 to 17 . 43 mbar / s ). the pressure at burst is a measure of seal quality . the results are reported in mbar . the results obtained in these tests are summarised in following table ii the speed of the bag - making machine has been decreased from 120 bags / minute to 100 , 90 , and 80 bags / minute and the seal power has been increased from 14 . 5 to 16 . 5 a and the results of the vphb for the film of comparative example 1 has always been below 50 mbar . a 6 - layer film differing from that of example 1 for the sealing layer comprising pec instead of pe1 was obtained according to the procedure described under examples 1 to 9 , irradiating at 75 kgy ( comparative example 11 ). by simply avoiding the corona treatment comparative example 12 was obtained . the two films have been converted into end seal bags and the cold seal strength and the hot seal strength have been evaluated as described under comparative examples 1 to 9 . the results obtained are reported in following table iii thus no improvement in the seal strength of the irradiated structure was observed when an ethylene - α - olefin with a density & lt ; 0 . 915 g / cm 3 was employed . 10 bags ( 300 × 500 mm ) were made with the film of example 1 and 10 bags of the same size were made with the film of comparative example 1 . they were all filled with 2 . 1 liter of water mixed with 20 cc of olive oil , sealed and tested in a simulated cook - in test where the bags were submerged in hot water at the temperature and for the time indicated in the following table iv . the film of example 14 is obtained by following the procedure of example 1 but corona treating at 450 ma instead of 240 ma . the seal quality of the obtained structure , evaluated by the parallel plates and the variable pressure hot burst tests , is slightly better than that of the structure of example 1 .