As a material...
give it lightness, like Mithril.
Give it... DR (small number)/magic
If you could make that overcome by fire instead of magic, that would be good, but officially that can't happen.
If you want it to be from the sticky kind of spiderweb, make it as follows:
If the wearer of this armor is attacked with a melee weapon (not natural weapons or unarmed strikes), and the attacker does not overcome the wearer's flat-footed AC, the attacker must make a Strength check that beats the armor's AC bonus, or be disarmed. If disarmed, the weapon sticks to the armor, and can be removed only with the same Strength check. Each failed Strength check that comes within 5 decreases the DC for future attempts to remove the same weapon by 1.