Mulch can be almost any loose aggregate material that will stay put and not significantly reduce air exchange out of the soil ...
Bulk mulch is less expensive than bagged mulch ... to the soil—in addition to the 2 to 3 F° already added by the bark mulch. "These can be boughs from evergreens or you can purchase evergreen ...
Pine bark is more acid (lower pH ... sold to commercial growers and potting soil manufacturers in bulk. Mulch processors sell fines by the semi load to growers and potting soil manufacturers.