Thistledown SuitLong used in the creation of light-weight padded armor by elven crafters, the silken fabric known as thistledown has recently been used in other armors as well by inventive halfling armorsmiths.
Any armor that normally incorporates an underlying layer of quilted fabric (including chain shirts, as well as any medium or heavy armor normally made of metal) can substitute a thistledown suit for the normal layer of fabric. This alteration increases the armor's armor check penalty by 1 (because of the added bulk) but reduces its arcane spell failure chance by 5% (because the quilted thistledown makes the armor less restrictive for somatic gestures).
A thistledown suit requires a DC 15 Craft (tailoring) check to create and costs 250 gp. It adds no weight to a suit of armor.