Brass or aluminium bodies with hardeded shackles to resist cutting. Usually use pins or disc wafers to secure the locking mechanism (with anywhere from 3 to 14). The better quality padlocks will have ball bearing locking mechanism, to resist shim attacks.
Some padlocks can have extra armor fitted to the external surface to prevent body attacks from sawing/cutting.
Closed shackle padlocks are also available to give extra protection against attack, along with long shackle padlocks which can be utilised in difficult locking situations.