Half a Drum Washes Better Than a Full One

A washing machine does not clean by soaking. It cleans by moving fabric through water, and an overfilled drum stops that movement almost entirely.

Mechanical action does most of the work

The drum lifts clothes and drops them back into the water. That repeated flexing pushes water through the fabric and dislodges soil from the fibres.

Detergent loosens the bond between soil and fibre, but something still has to carry the loosened soil away. That something is the movement of water through the cloth.

A drum packed to the top cannot lift anything. The load turns as a single mass, water moves around it rather than through it, and the interior of the load is barely washed.

Rinsing fails before washing does

The first casualty of overloading is the rinse. Clean water has to displace the detergent solution held in the fabric, and it can only do so if the fabric moves.

Detergent left in the cloth attracts soil afterwards, so clothes get dirty faster and develop a stiff feel that reads as a fabric problem rather than a washing one.

Skin irritation from washing is also frequently a rinsing failure rather than a reaction to the detergent itself. Less in the drum resolves it more often than changing product does.

The spin is also affected

An unbalanced or over-full drum cannot reach full spin speed, because the machine reduces speed to protect itself when the load is distributed unevenly.

A slower spin leaves more water in the clothes. They then take much longer to dry, and indoor drying puts that extra water into the flat as humidity.

An overloaded machine therefore causes a damp problem two rooms away, and the cause is rarely connected back to how the machine was filled.

How full is full enough

A useful test is whether a hand fits flat between the top of the load and the roof of the drum. If it does not, the load is too large.

Bulky items need more room than their weight suggests. Towels and bedding absorb a great deal of water and expand considerably once wet.

Delicate cycles need the drum emptier still, because they use gentler movement and rely on space for the clothes to move at all.

Underloading has its own cost

A near-empty drum wastes water, energy and detergent, and a single heavy item alone in the drum bangs against the sides and unbalances the spin.

Machines with load sensing adjust water to the weight, which reduces the waste but does not eliminate it. The fixed portion of each cycle is spent regardless.

Around two-thirds full is where the machine works as designed, and reaching that on a single household's laundry usually means washing less often rather than washing less.