There was a time when weight-inefficient steel was used for helmets (M1 'steel pot'). A helmet weighed about 2.85 lbs then.

Other (more weight-efficient) materials appeared, a kevlar helmet (PASGT-helmet) was adopted. Significant weight saving was possible. It weighed 3.1 to 4.2 lbs.

Then came MICH, with reduced coverage. It weighed a bit less than 3 lbs.

Then came ACH. It weighed 3 - 3.6 lbs.

The Marines introduced the LWH, at a medium version weight of 3.05 lbs.

More weight-efficient materials, roughly the same coverage - no loss of gear weight. In fact, now you can add a NVS' weight to a helmet.

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Rifle bullet-proofed body armour had its revival in the 90's; Dyneema used pressed PE, the Russians like titanium and steel plates, but most inserts used ceramic plates since.

Improvements in ceramics lead to better weight effectiveness, better multi-hit properties, higher rating (protection against SVD with AP, not just against AK with ball). Weight didn't drop, though.
Whenever there was some 'room for improvement' generated by 'weight savings', something was added. NIJ Level II basic vests instead of simple flak vests have been introduced. The front plate of the Ranger assault armour became the example for the ISAPO vest with back coverage as well. Interceptor improved protection again. Upper body side plates were invented & added, even some shoulder plates.

Again, vests have not significantly shedded their weight since 1995. The materials advanced and became more weight-efficient, but vests did not become lighter.

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There's a lot of buzz about "weight savings" for the "warfighter" blah blah, but all weight savings merely free up some weight for some other tool or toy.
Maybe it's human nature, maybe it's bureaucratic nature - or maybe political nature? In the end, there are no weight savings. There are additional tools ("capabilities") enabled by cutting weight off old tools.


Occasionally, some people fantasize about "light infantry" as "lighter individual load" infantry, even if only as a sidekick to heavy infantry of the conventional pattern. I did it several times as well.
It's hopeless. Auxiliaries may patrol & fight "light", but not our troops. They're Marius' mules and will stay so as long as we can afford their gear.