Cork is an impermeable buoyant material. It is the phellem layer of bark tissue which is harvested for commercial use primarily from Quercus suber (the cork oak), which is native to southwest Europe and northwest Africa. Cork is composed of suberin, a hydrophobic substance.

Auctions for wine corks sell in lots as small as 20 and as large as 500. The wine bottles usually sell for about 50 cents per bottle, but fancier bottles can fetch near $5.00 each (hint: Cobalt blue bottles!). Wine corks, however, generally sell for about 10 cents each.

The year 1680 has been stated as when the Benedictine monk first used cork for sealing wine. Previously stoppers had generally been made of wood wrapped in hemp soaked in olive oil. Cork was probably first used to seal wine in the sixth century BC (BCE) in Toscana (Tuscany).

I think the whole boiling and soaking thing is a holdover from the old days of winemaking. Back then corks were not very pliant and had to be softened by heat. In addition, water acted as a lubricant to help the corks get into the bottle. Also, corks were not very clean to begin with.