Are the tubes in your splice kits "Dual Wall" heat shrinkable tubing?

Yes!

All our heat shrinkable tubing splice kits have an inner adhesive lining which melts upon application of heat, thus serving to encapsulate the object while the tubing shrinks. This type of tubing is recommended for applications in which environmental conditions require sealing against moisture, such as submersed splices between the submersible pump motor and the pump cable. This adhesive also keeps out other contaminants in a wide variety of other applications.

Additional Resouces:

https://support.boshart.com/can-heat-shrink-splice-kits-be-used-in-underground-applications