Stopper with two opposite front sides, comprises a core and optionally one or more layers enclosing the core, where the stopper comprises: (a) a core of a plastic material from one or more polymers with a high resilience comprising e.g. polyphenylene oxide, or polyethylene copolymers； (b) optionally one or more intermediate layer(s) of a plastic material of one or more polymers of e.g. functionalized polypropylene, or styrene/ethylene/propylene copolymer； and (c) optionally an outer layer of a plastic material of one or more polymers of e.g. polyester, or polyethylene plastomer. Stopper with two opposite front sides, comprises a core and optionally one or more layers enclosing the core, where the stopper comprises: (a) a core of a plastic material from one or more polymers with a high resilience comprising polyphenylene oxide, polyethylene copolymers, ethylene vinyl acetate, styrene/ ethylene/butylene block copolymer, styrene/ethylene/propylene copolymer, polypropylene, medical white oil, styrene/butadiene/styrene copolymer, polybutylene, ethylene/propylene/diene-rubber, ethylene/propylene plastic, or styrene/butadiene/styrene block polymer； (b) optionally one or more intermediate layer(s) of a plastic material of one or more polymers of functionalized polypropylene, polyethylene, functionalized styrene/ ethylene/butylene block copolymer, polyethylene plastomer, polyethylene copolymer, ethylene-vinyl acetate, styrene/ethylene/propylene copolymer, oil, polypropylene, polyethylene, styrene/isoprene/styrene block copolymer, or polybutylene； and (c) optionally an outer layer of a plastic material of one or more polymers of polypropylene, polyester, polycarbonate, polyethylene copolymer, polyethylene plastomer, ethylene vinyl acetate, poly(cyclohexylene dimethylene cyclohexanedicarboxylate), glycol and acid comonomer or styrene/ ethylene/butylene block copolymer/styrene/ethylene/propylene copolymer, polymethylpentene, polybutylene, and/or soft PVC, where the material of
