This lightweight fabric gets its name from its soft feel and dove-grey colour. Elves have made padded armour from this material for centuries, and it is well-liked by arcane spellcasters.
Thistledown padded armour weighs only half as much as normal padded armour. It grants its wearer a +2 circumstance bonus on Hide checks in areas of darkness or shadowy illumination, as it blends in with the dim background. It is treated as masterwork armour (the masterwork cost is included in the armour’s given cost).
Thistledown has 2 hit points per inch of thickness and hardness 0.
Source: Races of the Wild (Page 168)