
Bahne |

The section pertaining to the Damage Reduction values of specific enhancement bonus weapons are as follows... (see it on page 562)
DR TYPE & Weapon Enhancement Bonus Equivilent
cold iron/silver +3
adamantine* +4
alignment based +5
*Note that this does not give the weapon the ability to ignore hardness like an actual adamantine weapon does.
Thusly a character with a +3 Defending Sai could bypass the DR's of opponents with Cold Iron/Silver (regardless of what the weapons made from) as long as he doesnt transfer ANY of the weapons enhancement in that round to AC, if he does, then his attacks will only function vs DR/Magic as a plain magic weapon.
So unless said Sai is already crafted from special materials, then the odds of him usefully employing it against dangerous opponents even in this defesive fashion are limited.
cheers! :)