A method for manufacturing a closure for a product-retaining container constructed for being inserted and securely retained in a portal-forming neck of said product-retaining container, said method comprising at least the following method steps: i. intimately combining the following components, to form a composition: (a) 51 to 80 wt.% (dry weight) or 51 to 85 wt.% (dry weight) of a plurality of coated particles, said coated particles each comprising a core comprising cork material and at least one outer shell comprising a first plastic material, said first plastic material comprising one or more thermoplastic polymers; (b) 12 to 49 wt.% of a second plastic material comprising one or more thermoplastic polymers; (c) optionally 0 to 10 wt.% of one or more blowing agents; (d) optionally, 0 to 15 wt.% of one or more lubricants; (e) optionally, 0 to 2 wt.% of one or more pigments; and (f) optionally, 0 to 10 wt.% of one or more additives and/or fillers; ii. heating the composition obtained in step i. to form a melt; iii. forming, by means of extrusion or molding, a closure precursor from the melt obtained in step ii; and iv. optionally cutting and/or finishing the closure precursor to form the closure; or said method comprising at least the following method steps: i. intimately combining the following components, to form a composition: (a) 52 to 100 wt.% (dry weight) of a plurality of coated particles, said coated particles each comprising a core comprising cork material and at least one outer shell comprising a first plastic material, said first plastic material comprising one or more thermoplastic polymers; (b) 0 to 48 wt.% of a second plastic material comprising one or more thermoplastic polymers; (c) optionally 0 to 10 wt.% of one or more blowing agents; (d) optionally, 0 to 15 wt.% of one or more lubricants; (e) optionally, 0 to 2 wt.% of one or more pigments; and (f) optionally, 0 to 10 wt.% of one or more additives and/or fillers; ii. heating the composition obtained in step i. to form a melt; iii. forming, by means of extrusion or molding, a closure precursor from the melt obtained in step ii; and, iv. optionally cutting and/or finishing the closure precursor to form the closure. i. intimately combining the following components, to form a composition: (a) 51 to 80 wt.% (dry weight) or 51 to 85 wt.% (dry weight) of a plurality of coated particles, said coated particles each comprising a core comprising cork material and at least one outer shell comprising a first plastic material, said first plastic material comprising one or more thermoplastic polymers; (b) 12 to 49 wt.% of a second plastic material comprising one or more thermoplastic polymers; (c) optionally 0 to 10 wt.% of one or more blowing agents; (d) optionally, 0 to 15 wt.% of one or more lubricants; (e) optionally, 0 to 2 wt.% of one or more pigments; and (f) optionally, 0 to 10 wt.% of one or more additives and/or fillers; (a) 51 to 80 wt.% (dry weight) or 51 to 85 wt.% (dry weight) of a plurality of coated particles, said coated particles each comprising a core comprising cork material and at least one outer shell comprising a first plastic material, said first plastic material comprising one or more thermoplastic polymers; (b) 12 to 49 wt.% of a second plastic material comprising one or more thermoplastic polymers; (c) optionally 0 to 10 wt.% of one or more blowing agents; (d) optionally, 0 to 15 wt.% of one or more lubricants; (e) optionally, 0 to 2 wt.% of one or more pigments; and (f) optionally, 0 to 10 wt.% of one or more additives and/or fillers; ii. heating the composition obtained in step i. to form a melt; iii. forming, by means of extrusion or molding, a closure precursor from the melt obtained in step ii; and iv. optionally cutting and/or finishing the closure precursor to form the closure; or i. intimately combining the following components, to form a composition: (a) 52 to 100 wt.% (dry weight) of a plurality of coated particles, said coated particles each comprising a core comprising cork material and at least one outer shell comprising a first plastic material, said first plastic material comprising one or more thermoplastic polymers; (b) 0 to 48 wt.% of a second plastic material comprising one or more thermoplastic polymers; (c) optionally 0 to 10 wt.% of one or more blowing agents; (d) optionally, 0 to 15 wt.% of one or more lubricants; (e) optionally, 0 to 2 wt.% of one or more pigments; and (f) optionally, 0 to 10 wt.% of one or more additives and/or fillers; (a) 52 to 100 wt.% (dry weight) of a plurality of coated particles, said coated particles each comprising a core comprising cork material and at least one outer shell comprising a first plastic material, said first plastic material comprising one or more thermoplastic polymers; (b) 0 to 48 wt.% of a second plastic material comprising one or more thermoplastic polymers; (c) optionally 0 to 10 wt.% of one or more blowing agents; (d) optionally, 0 to 15 wt.% of one or more lubricants; (e) optionally, 0 to 2 wt.% of one or more pigments; and (f) optionally, 0 to 10 wt.% of one or more additives and/or fillers; ii. heating the composition obtained in step i. to form a melt; iii. forming, by means of extrusion or molding, a closure precursor from the melt obtained in step ii; and, iv. optionally cutting and/or finishing the closure precursor to form the closure.