Dilute Jello works best since it is part sugar part protein. A full bladder is a place for extra heat loss. You will need to help the person urinate. Add Heat Hot water bottles, hot pads, etc. to transfer heat to major core arteries - neck, armpits, groin, palms of hands. If peripheral vessels open up, cold acidic blood from periphery goes to core - may cause heart arrhythmias and death.
Ice crystals form in cells.
If hot - can burn damaged skin. Thawing is complete when part is pliable and colour and sensation return. Once area has rewarmed, there can be considerable pain. Wrap affected area in sterile gauze and protect from movement and further cold. Treat as a tissue injury - consider hospital if significant tissue damage.