The distinction between compression springs and other types of springs is that they are designed to bear a load that compresses the spring, causing the spring to get shorter and increase in tension as it stores more mechanical energy.
Different compression spring manufacturers may use different kinds of metals. For example, a manufacturer may use pre-hardened metal to wind small compression springs, while they may use softer metal for larger ones and harden the metal after winding. Compression springs that need to be especially resistant to corrosion may be made of galvanized wire.