Bottle sealer serving as a temperature buffer

A bottle sealer made of elastomer materials sealably inserted in a bottleneck of a bottle comprising:

• an inner annular portion sealably inserted in a bottleneck;
• a cylindrical skirt portion protruding outwardly from said inner annular portion to seal an outer edge of the bottleneck;
• and a telescopic expansible hollow extension joined to said inner annular portion having one end portion of said extension closed and having means for contacting a liquid filled inside the bottle and operatively expansible within the bottleneck when subjected to a cold environment temperature below zero degree centigrade for absorbing a volume expansion of the liquid inside the bottle, without breaking the bottle made of glass or the like;
• said telescopic expansible hollow extension including a flip-flop extension concave outwardly from the inner annular portion to form an outer cylinder portion defining an outer edge of the outer cylinder portion which is then convex inwardly opposite to an outer edge of the bottleneck to form an inner cylinder portion having a base portion generally coplanar to a surface of the inner annular portion, a cylindrical aperture being defined between the inner cylinder portion and the outer cylinder portion of said hollow extension, said base portion of said inner cylinder portion being embedded with a transparent bottom plate therein.