HEre it is:<br/><br/>After being treated alchemically, this material is almost always woven into a masterwork silk tunic (included in the cost). This is considered padded armor but it can be worn under any other type of armor adding no weight and offering DR 3/slashing and bludgeoning. The price of items crafted of aranea silk is increased by +1,150 gp.<br/><br/>*  *  *<br/><br/>So the effect is that it negates three points of damage from piercing attacks.  USed on it's own, it's padded armor.  Alternatively it can be integrated into a heavy armor as it's padding.<br/><br/>That's a pretty nice item.  (Of course, it IS third party.)