Phospholipid Bilayer
Cell membranes composed of phospholipids
The cell membrane is a double-walled structure containing a cell's genetic code.
A cell that is double walled is a plant cell. This is because the plant cells can't move so they need extra protection.
Luxury caskets often have a double lid, sometimes even a triple lid (the innermost being made of glass). In rare cases, caskets are even double walled (triple walled would be absolutely unusual), which means that the outer casket contains a complete inner casket, which can be taken out. Double walled caskets are much more heavy than double lid caskets, of course.
Pericardium
Serous membrane
A double phospholipid bilayer surrounds the nucleus.
Amniotic sac
That thick, doubled walled, peptidoglycan cell wall!
mitochondrion
Ice is readily available for them, and it is a good insulator.
Such organelles are called mitochondria.