SYSTEM REFERENCE DOCUMENT 3.5
Iron, Cold: This iron, mined deep underground, known for its effectiveness against fey creatures, is forged at a lower temperature to preserve its delicate properties. Weapons made of cold iron cost twice as much to make as their normal counterparts. Also, any magical enhancements cost an additional 2,000 gp.
Items without metal parts cannot be made from cold iron. An arrow could be made of cold iron, but a quarterstaff could not.
A double weapon that has only half of it made of cold iron increases its cost by 50%.
Cold iron has 30 hit points per inch of thickness and hardness 10.