Different tensions for Nylon, Poly, Blends?

[M.Kowalski]

I've heard in passing this example (string material used for example only): If a racquet is strung with Nylon at 60lbs. to get the same feel/tension with a poly you need to string +2lbs. and a blend -2lbs. --or, something like that. Does anyone know about such a "rule of thumb"? Thanks.

[Jens]

The rule of thumb is this: The less elastic the string, the less tension you should use on it. The order is the following (high elasticity first):
Natural Gut
Multifilament Strings
Nylon Strings
Polyester Strings
Aramid (as used in Hybrid strings)

While you can string natural gut, multifilaments and nylon string (and even thin soft polyester strings) at around the same tension, you should use about 1-2 lbs less tension on polyester strings (the thicker, the less tension) and at least 2-4 less tension on Aramid/Kevlar strings.