Exactly how much protection would a cotton gambeson with 0.9 inches of padding worn under the non metal reinforced 14th century cuirass (item #AA1000C) featured below:

http://www.schmitthenner.com/cuirass.htm#Medieval%20Styles

provide? Apart from blunt traume prevention, would the above ensemble be of any use against sharp bladed weapons?

Would thick whole leather over thick padding be more effective than leather lamellar over similar padding?

In the brief period of time in which cuirassses like that were worn they were worn exclusively in conjunction with mail. The mail gauranteed the protection from the cut. The leather served mostly to provide blunt trauma protection and to reinforce the cut- and puncture-resistance of the mail.

If you're looking for a more exact figure then I will answer: 7

Cheers,
Steven

Virtually every culture that had a textile iundustry made use of standalone textile armour. The most effective consisted of multiple layers quilted together. If it was intended to be worn with another type of armour then it was a lot lighter and flexible than if it was intended to be worn by itself. The two are very different garments and people confuse them all the time. We need to use separate terms to help classify them. I'd like to see the word gambeson reserved for standalone armour while haketon is used for underarmour. As Steven mentioned, the above cuirass was not worn with either type of padded defense - it was worn over mail while the mail would have been worn over a light haketon.

We need terms to classify different types of armour. Best to use original terms but often there is no consistency. Doesn't really matter so long as everyone applies the same definition to the same terms. Gambeson is more often used to describe a standalone armour than an under-armour so that is what I prefer to use. Haketons and especially pourpoints are usually used in the sources to describe under-armour. If you get hung up on the original text then you are wasting your time. The most common term is lorica which simply means "armour". Doesn't help at all.

The clash between taxonomic language, common modern usage, and period usage can be problematic, but only if the writer/reader doesn't distinguish between these 3 types of usage (explicitly, or at least by clear context).

One can always use unambiguous descriptors such as "type 1", "type 2", etc., but it's impenetrable to the uninitiated.

Also hard to establish consistent usage from the bottom-up, since a single writer or group only controls a small part of the bottom. The effective method is to write the classic monograph on the subject, and then your classification scheme will be used if useful.