Hiya,
Spirit Webbing is only applicable to biped armour and it offers +10 ethereal armour for each application. It is the only way to make crafted gear with ethereal armour, and as a negative consequence each application applies a strength modifier of -2.
It is a rarity, but in terms of practical use there are specific monsters where it is ideal to use because they inflict ethereal damage, other times it is best to stick to your conventional armour.