The surprising afterlife of used hotel soap

[ProfessorGAC]

39. It's Not Just That

Most bar soaps are synthetic detergent or a mix of soap & detergent. (There's a chemical difference between soap & detergent.)
But, the predominant surfactant in bar soap are isethionates. These are not heavy duty surfactants, so using them in a washing machine is inherently less effective.
Those are also higher foam surfactants & the lower water usage of HE machines could lead to less thorough rinsing.
The first reason makes it a poor plan in any kind of machine. The second makes it an even worse idea for HE machines.
One more consumer fact: the heavier duty surfactants in laundry formulas have never been high foaming, so there's almost no difference HE detergents & those not marked HE. The only difference between premium & discount brands is water. A product like Tide has 20% more active ingredients than something like Surf. And the real discount brands are probably around 60% of Surf.
Laundry detergents are an actual example of "you get what you pay for".