This is the single most common complaint in the category and it is almost always designed in rather than caused by the owner.

Where the moisture goes

Damp kit in a closed bag has nowhere to release moisture to, so it goes into the bag. An unlined woven fabric absorbs it into the weave, where it stays for as long as the bag is shut.

That is why the smell survives emptying the bag and airing the room. The bag itself is damp, not the contents.

Why a coated lining changes it

A coated lining is not absorbent. Moisture beads and sits on the surface, where it evaporates when the bag is opened or wipes off in one pass.

It also gives you a cleanable surface. You cannot meaningfully clean the inside of an unlined nylon body; you can wipe out a coated one in under a minute.

Why venting matters more than people think

Even a lined bag needs to dry. Air moving through the bag is what removes the moisture that the lining refused to absorb.

One mesh panel does not do this. Air needs an inlet and an outlet, so mesh at opposite ends of the bag is the specification — and it costs almost nothing to add at the point of manufacture and cannot be added afterwards.

The wet compartment is the other half

Keeping the damp things in one lined, vented, properly seamed compartment stops the moisture reaching the rest of the bag at all.

Check the seam. If it stops short of the top of the divider, the compartment is decorative and the water is going into the main body anyway.

What cleaning can and cannot do

Wiping out a coated lining works. Washing an unlined bag helps for a fortnight.

If a bag has to be rescued regularly to be usable, the bag is wrong. This is a specification problem, and it is fixed at the quote rather than at the sink.