What's the difference between a hair mask and a bond-building treatment?

A traditional hair mask (like the Arvazallia or Karseell picks) is a rinse-out deep conditioner focused on moisture and surface smoothing. Bond-building treatments such as Olaplex and K18 target the internal disulfide and keratin-chain damage caused by bleach, color and heat. Many people who color or heat-style use both: a bond treatment to repair structure and a moisture mask to soften and seal. The verified-purchase reviews we read frequently mention pairing the two.