Isoleren verbetert het energielabel.

Isoleren is the infinitive of the verb isoleren, meaning to insulate.

In this sentence, the infinitive is being used as the subject of the sentence, so it works a bit like English insulating or to insulate in:

• Insulating improves the energy rating
• To insulate improves the energy rating
  (this is less natural in English, but it shows the structure)

So isoleren here is not a finite verb. It is the thing being talked about.

Because the subject is isoleren, and that whole infinitive idea is treated as a singular subject.

So Dutch uses the third-person singular form of the verb:

• isoleren verbetert
• not isoleren verbeteren

This is similar to English:

• Insulating improves the energy rating
• not Insulating improve

Because isoleren is not part of a verb phrase like to improve or to insulate after another verb. Here it is being used on its own as the subject.

Compare:

• Isoleren verbetert het energielabel.
  = Insulating improves the energy label.

But:

• Het is belangrijk om te isoleren.
  = It is important to insulate.

In the second example, te isoleren is part of an infinitive construction. In your sentence, isoleren is simply the subject, so there is no te.

Because energielabel is a het-word in Dutch.

So you say:

• het energielabel
• een energielabel

Many compound nouns take the gender of the main noun, and here the main noun is label, which is a het-word:

• het label
• therefore het energielabel

Yes. Dutch very often writes compound nouns as one word.

So:

• energie
  • label = energielabel

This is very normal in Dutch. English often uses separate words where Dutch prefers compounds.

Other similar examples:

• woonkamer = living room
• fietsbel = bicycle bell
• energierekening = energy bill

Not usually in this context. In everyday Dutch, energielabel often means an energy-efficiency rating or energy performance certificate/classification, especially for houses and buildings.

So in this sentence, it usually means that better insulation improves the building’s energy-efficiency classification.

Depending on context, a more natural English translation may be:

• Insulation improves the energy rating.
• Insulating improves the energy-efficiency label.

Het energielabel is the direct object of the verb verbetert.

Structure of the sentence:

• Isoleren = subject
• verbetert = finite verb
• het energielabel = object

So literally:

• Insulating
  • improves
    • the energy label

Because this is a normal main clause in Dutch, and Dutch main clauses usually follow the V2 rule: the finite verb comes in the second position.

Here the first position is occupied by the subject Isoleren, so the finite verb comes next:

• Isoleren | verbetert | het energielabel

If something else came first, the verb would still stay in second position:

• Door te isoleren verbetert het energielabel.
• Met goede isolatie verbetert het energielabel.

So the sentence is following standard Dutch main-clause word order.

Yes. That is also a natural sentence.

There is a slight difference in feel:

• Isoleren verbetert het energielabel focuses on the action/process of insulating.
• Isolatie verbetert het energielabel focuses more on insulation as a thing or material/system.

Both can work, depending on context.

Yes. The infinitive is verbeteren, meaning to improve.

Present tense conjugation:

• ik verbeter
• jij verbetert
• hij/zij/het verbetert
• wij/jullie/zij verbeteren

In your sentence, the subject behaves as singular, so the form is verbetert.

A natural past-tense version would be:

• Isoleren verbeterde het energielabel.

Here:

• verbetert = present tense
• verbeterde = past tense

So:

• Isoleren verbetert het energielabel. = Insulating improves the energy rating.
• Isoleren verbeterde het energielabel. = Insulating improved the energy rating.

Roughly: ee-soh-LAY-ren.

A few helpful notes for English speakers:

• i in the first syllable sounds like ee
• o is a clear Dutch o
• -ren is not pronounced like English run
• the r may sound different depending on region

A rough English-friendly approximation is:

• ee-zo-LAY-run

But listening to native audio is best, especially for the Dutch vowels and r.