Tae Kim describes it as meaning "assume [we] verb" but that doesn't always make sense to me. - http://www.guidetojapanese.org/reasoning.html#part3

ふわふわ。その名のとおりふわふわっとした内容です。

"Fluffy" (name of a book). In parallel with the name, the contents assumed fluffy.

Is とした a completely different grammar to とする? Can somebody sum up what they both mean?

Virtua_Leaf Wrote:Tae Kim describes it as meaning "assume [we] verb" but that doesn't always make sense to me. - http://www.guidetojapanese.org/reasoning.html#part3

ふわふわ。その名のとおりふわふわっとした内容です。

"Fluffy" (name of a book). In parallel with the name, the contents assumed fluffy.

Is とした a completely different grammar to とする? Can somebody sum up what they both mean?

There are many forms of と+する constructs indeed. I hardly know all of them, but I know many enough to say that とした and とする could definitely be different things.

For example, として means "as". IE:

彼は学者として立派だが、人間として尊敬できない。
"He is great as a scholar, but as human I can't respect him".

Tobberoth Wrote:

Virtua_Leaf Wrote:Tae Kim describes it as meaning "assume [we] verb" but that doesn't always make sense to me. - http://www.guidetojapanese.org/reasoning.html#part3

ふわふわ。その名のとおりふわふわっとした内容です。

"Fluffy" (name of a book). In parallel with the name, the contents assumed fluffy.

Is とした a completely different grammar to とする? Can somebody sum up what they both mean?

There are many forms of と+する constructs indeed. I hardly know all of them, but I know many enough to say that とした and とする could definitely be different things.

For example, として means "as". IE:

彼は学者として立派だが、人間として尊敬できない。
"He is great as a scholar, but as human I can't respect him".

Oh yeah, I think I learned about that として/as. としては = a comparative "for" or simply and "as for", while　としても means... was it "even if"? Also there's the 'attempt to do' grammar when used with the volitional form.

But all these special conjugated forms and I still don't know what とする means! Nearly 62 millions results come up for it in Google as well.

This is not unusual.

While studying for JLPT2, I notice that around 20% of the grammar constructs have no direct translation in English. In other words, if you come up with an English translation, your translation will either be too broad (some usage in English is no good in Japanese), too narrow (your translation in English doesn't cover some usages in Japanese), or both (no joke)!!!

So what I do to study these cases is to have a translation just to get a rough idea of the usage, but then have plenty of clear examples of usage. In other words, don't get too stuck on a diect translation, but at least understand the gist of your sentence.

Getting back to your question. とする in its many forms fits into my 20% fuzzy list. In どんな時どう使う日本語表現文型辞典, there are actually different variants: としたら、　として、として～ない、としても、とすると、and とすれば, so you actually need to study the forms for とする separately. It also mentions that としたって is like としても or にしたところで。 としたところで　is like にしたところで。　If you look at another source, you will get a different list.

Specifically, for として, the entry says　～の立場で　～の資格で　～の名目で

Now, if you can remember all that, you are a better student than I am!!! Even though I have yet to try it, grammar is one of those cases where I think AJATT may be a much better way to study. You can try to study the grammar to understand or translate a sentence into English, but it may be quite difficult to produce sentences fluently, unless you just learn patterns and let them sink in naturally (the sooner the better). For me, many of the JLPT2 grammar patterns seem to be like this.

In ugly cases, I ask a native or an instructor rather than spending too much time trying to guess (wrongly).

This post probably didn't answer your question, but hopefully, it explains what's going on...

According to A Dictionary of Intermediate Japanese Grammar, "とする" can mean "feel ~; look ~". In the Notes section it says:

"Sound-symbolical word + to suru is used to mean 'to look ~' or 'to feel ~.'"

It gives lots of examples too. It seems to be what you're looking for here, I think.

I find generative constructions easier to understand.
So, what about a generative view of the sentence, instead of a descritive view?

Even する is not the verb "to do". It has a very different meaning. For some things it is more general, for some things is is narrower.

彼は学者として立派だが、人間として尊敬できない。

One can stress the generality of する and use the と as a conditional here.
(please don't flame me, I'm only trying to use my imagination, this was only a matter of personal taste)

As others stated, a lot of times you can't make direct translations with Japanese grammar. The closest way to 'translate' とした in this case is to think of how quotations can be used in English.

First let's look at your sentence and see what it really means

ふわふわ。その名のとおりふわふわっとした内容です。

The author is trying to state that the book itself is "fluffy", as the title of the book infers. So a closer translation would be something like: "Like the title, the book itself is very "fluffy".

Like quotations, とする/とした emphasizes how something looks or feels, as Kaede stated. A common construction is to see とした顔, to describe somebody's expression.

Here are a few examples I pulled from ALC:

あなた、ボーッとした顔しているけど、ちゃんと聞いているのね！
You look so blank but you're paying attention!

ホッとした顔をする
To show an expression of relief.

In the same vein, さわさわとした内容 is simply trying to define the feel of the book in a concrete manner.

Hope this helps =)

It really does.

Thanks everyone, this has been extremely helpful.