Il cappotto termico funziona a condizione che copra tutto.

Because a condizione che normally requires the subjunctive in Italian.

• copre = indicative
• copra = present subjunctive

So:

• Il cappotto termico funziona a condizione che copra tutto.

means The thermal coat works provided that it covers everything, and the clause after a condizione che is treated as a condition, so Italian uses the subjunctive.

A condizione che means provided that, on condition that, or as long as.

It is a perfectly normal and correct expression, though it can sound a little more formal than some alternatives.

Other similar expressions are:

• purché = provided that / as long as
• a patto che = on condition that

All of these are typically followed by the subjunctive.

For example:

• Funziona purché copra tutto.
• Funziona a patto che copra tutto.

The subject of copra is still il cappotto termico.

So the structure is:

• Il cappotto termico = subject
• funziona = main verb
• a condizione che copra tutto = conditional clause

Literally, it is saying:

• The thermal coat works, provided that it covers everything.

Italian often leaves the subject unstated in the second clause because it is already clear from context.

If you wanted to make it explicit, you could say:

• Il cappotto termico funziona a condizione che esso copra tutto.

But that sounds unnecessarily heavy. Normally, you would just say copra.

Because Italian is a pro-drop language, which means subject pronouns are often omitted when the verb ending already shows the person and number.

In English you must say:

• provided that it covers everything

In Italian, the verb form often makes the subject clear enough on its own:

• a condizione che copra tutto

The it is understood from the context.

Here, tutto means everything, so it is a pronoun, not an adjective modifying a feminine noun.

Compare:

• copra tutto = covers everything
• copra tutta la schiena = covers the whole back
• copra tutto il corpo = covers the whole body

So:

• tutto = everything / the whole thing
• tutta = whole feminine singular noun
• tutti / tutte = all / whole plural forms

In your sentence, tutto is correct because nothing follows it; it stands alone and means everything.

Italian uses the definite article much more often than English.

So where English might say:

• Thermal coat works... (though this sounds incomplete in English too)

Italian normally says:

• Il cappotto termico...

The article il means the and is the normal choice here.

Yes, termico is the direct equivalent of thermal in many contexts.

So:

• cappotto termico = thermal coat / thermal jacket / insulating coat

That said, the most natural translation can depend on the context. In some situations, Italian might also use wording based on function rather than a literal adjective.

Still, grammatically, cappotto termico is fine.

Yes. Funzionare often means to work, to function, or to do its job.

It is very commonly used not only for machines, but also more generally for things that are effective.

So here funziona means something like:

• works
• does its job
• is effective

If the context is practical or technical, this sounds natural.

You could say se copre tutto, but it is not exactly the same.

• se copre tutto = if it covers everything
• a condizione che copra tutto = provided that it covers everything / on condition that it covers everything

The second version emphasizes a requirement or condition more strongly.

So:

• Funziona se copre tutto = more neutral, simple if
• Funziona a condizione che copra tutto = more formal or explicit condition

Copra is the present subjunctive of coprire.

Here is the present subjunctive of coprire:

• che io copra
• che tu copra
• che lui/lei copra
• che noi copriamo
• che voi copriate
• che loro coprano

In your sentence, copra could correspond to:

• that I cover
• that you cover
• that he/she/it covers

But from the context, it clearly means it covers.

Because a condizione che is a fixed expression meaning provided that or on condition that.

You should learn it as a complete chunk:

• a condizione che + subjunctive

The che introduces the subordinate clause:

• a condizione che copra tutto

This is very common in Italian with conjunction-like expressions:

• prima che
• senza che
• benché
• a patto che
• purché

Many of these trigger the subjunctive.

A simple pronunciation guide is:

eel kahp-POHT-toh TEHR-mee-koh foon-TSYOH-nah ah kohn-dee-TSYOH-neh keh KOH-prah TOOT-toh

A few useful pronunciation points:

• cappotto has a double pp, so hold the consonant slightly longer.
• termico has stress on ter.
• funziona sounds roughly like foon-tsyoh-na.
• condizione has the tsi sound: kon-di-tsyoh-ne.
• che here sounds like keh.
• copra has stress on the first syllable: KOH-pra.
• tutto has a double tt, again with a slightly stronger consonant.

It sounds mostly neutral to somewhat formal because of a condizione che.

The grammar is completely normal, but that phrase is a little more formal than everyday casual speech.

A more conversational version might be:

• Il cappotto termico funziona se copre tutto.

A more compact but still fairly natural version could be:

• Il cappotto termico funziona purché copra tutto.

So the original sentence is correct and natural, especially in explanatory, technical, or written contexts.