The Thermal Shield Xpander Pak Foam Expansion Mailer is a top-of-the-line RX2 type expandable mailer. It is used for superior cushioning and temperature sensitive products. It uses a high-density polyurethane foam that is compressed to 3/8th of its original size. Insert your items into the Xpander Pak, seal it using the self-adhesive strip, and expand it by making a small puncture with a pen. The vacuum foam lining expands to six times its size and offers extreme protection for your temperature sensitive and fragile items. This expanding mailer features the densest foam and provides the longest thermal protection available.