Το πάπλωμα είναι βαρύ, αλλά πολύ ζεστό.

Το is the definite article, meaning the.

In this sentence, το πάπλωμα means the duvet / the quilt.
The article το tells you that πάπλωμα is:

• neuter
• singular

Here, το πάπλωμα is the subject of the sentence, so it is in the nominative case.

A useful detail: for many neuter nouns in Greek, the nominative and accusative singular look the same, so you often identify the case from the noun’s role in the sentence.

Πάπλωμα is a neuter noun.

It belongs to a very common Greek pattern: nouns ending in -μα are often neuter. Other common examples are:

• το γράμμα = the letter
• το όνομα = the name
• το πράγμα = the thing

The plural of πάπλωμα is παπλώματα.

So:

• το πάπλωμα = the duvet
• τα παπλώματα = the duvets

Είναι is the present-tense form of είμαι, which means to be.

Here it means is:

• Το πάπλωμα είναι βαρύ. = The duvet is heavy.

A useful thing to know is that είναι is also used for they are in Modern Greek:

• Αυτό είναι... = This is...
• Αυτά είναι... = These are...

So είναι can mean either is or are, depending on the subject.

Because they are not directly attached to the noun inside the noun phrase. They are used after the verb είναι, so they are predicate adjectives.

Compare:

• το πάπλωμα είναι βαρύ = the duvet is heavy
• το βαρύ πάπλωμα = the heavy duvet

In your sentence, the structure is:

• subject: Το πάπλωμα
• verb: είναι
• adjectives: βαρύ, πολύ ζεστό

So this works just like English The duvet is heavy, but very warm.

Because Greek adjectives must agree with the noun they describe in:

• gender
• number
• case

Since πάπλωμα is neuter singular, the adjectives also appear in the neuter singular form.

That is why you get:

• βαρύ = heavy, neuter singular
• ζεστό = warm, neuter singular

For example:

ζεστός adjective:

• ζεστός = masculine
• ζεστή = feminine
• ζεστό = neuter

So:

• ο καφές είναι ζεστός = the coffee is warm
• η σούπα είναι ζεστή = the soup is warm
• το πάπλωμα είναι ζεστό = the duvet is warm

Βαρύ is from the adjective βαρύς, which is a less regular pattern:

• βαρύς = masculine
• βαριά = feminine
• βαρύ = neuter

Here πολύ means very, so it is being used as an adverb modifying ζεστό.

• πολύ ζεστό = very warm

When πολύ works as an adverb, it does not change to agree with gender or number.

Compare:

• πολύ ζεστό = very warm
• πολύ βαρύ = very heavy
• πολύ καλή = very good

In all of those, πολύ stays the same.

This is different from adjective uses such as much/many, where Greek has agreeing forms like:

• πολύς
• πολλή
• πολύ

But in your sentence, it is simply the adverb very.

It can be repeated, but it does not have to be.

Greek often leaves out words that are easily understood from the context. So:

• Το πάπλωμα είναι βαρύ, αλλά πολύ ζεστό.

really means:

• Το πάπλωμα είναι βαρύ, αλλά είναι πολύ ζεστό.

The second είναι is omitted because the meaning is already clear.

This is very natural Greek.

Αλλά means but.

It introduces a contrast:

• βαρύ = heavy
• αλλά πολύ ζεστό = but very warm

The comma before αλλά is normal Greek punctuation when joining contrasting parts of a sentence like this.

So the structure is:

• X, αλλά Y = X, but Y

A rough pronunciation is:

to PA-plo-ma EE-ne va-REE, al-LA po-LEE ze-STO

More naturally in Modern Greek pronunciation:

to PÁ-plo-ma Í-ne va-RÍ, al-LÁ po-LÍ ze-STÓ

The stress falls on:

• πάπλωμα
• είναι
• βαρύ
• αλλά
• πολύ
• ζεστό

The written accent mark in Greek shows you which syllable is stressed.

Yes. Greek word order is more flexible than English, although the version you have is the most neutral and natural one.

Your sentence:

• Το πάπλωμα είναι βαρύ, αλλά πολύ ζεστό.

A speaker could also rearrange things for emphasis, for example:

• Το πάπλωμα είναι πολύ ζεστό, αλλά βαρύ.

That changes the emphasis slightly: now very warm comes first, and heavy is the contrasting point.

So the original sentence is a straightforward, neutral way to say it.

Yes, but that would be a different structure.

• Το πάπλωμα είναι βαρύ, αλλά πολύ ζεστό.
  = The duvet is heavy, but very warm.

This is a full sentence with είναι.

• ένα βαρύ αλλά πολύ ζεστό πάπλωμα
  = a heavy but very warm duvet

This is just a noun phrase, not a full sentence.

So Greek can express the same idea in two ways:

1. Predicative

   • Το πάπλωμα είναι βαρύ.
   • The duvet is heavy.

2. Attributive

   • το βαρύ πάπλωμα
   • the heavy duvet

That distinction is very useful in Greek.