Why some Litz wire is difficult to strip

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: "Scott Hanson by way of Terry Fritz <twftesla-at-qwest-dot-net>" <huil888-at-surfside-dot-net>

There are many different types of insulating "varnish" applied to magnet wire,
depending on the application: temperature requirements, environmental exposure,
bend radius, voltage, processing requirements, polymer type, etc, etc.
 
Insulating coatings can be broken down into many different groups. One possible
grouping is based on how the wire is stripped for soldering. One group
(including the very common "Formvar" varnish, Polythermaleze, etc) requires
mechanical or chemical removal of the coating. Even extended immersion in a
solder pot with highly activated flux WILL NOT remove this type of coating and
allow the wire to "tin".
 
Other coatings ("Sodereze" "Nyleze", etc) are specifically designed to allow
tinning in a solder pot. Often this results in somewhat of a trade-off of
thermal, mechanical, or chemical resistance. 
 
In my experience, the thickest, toughest, most robust, highest temperature
insulation will always be the most difficult to strip & tin.
 
This probably explains why some users find their wire easy to tin, and others
find it almost impossible, especially with surplus wire that may not have the
insulation identified.
 
Scott Hanson