Эта майка из хлопка, поэтому в ней удобнее, чем в майке из шёлка.

Not quite.

Майка usually means a tank top, undershirt, or sleeveless shirt.
Футболка is a T-shirt, usually with sleeves.

So in this sentence, майка is specifically a sleeveless garment, not just any shirt.

Because майка is a feminine singular noun.

The demonstrative this must agree with the noun in gender, number, and case:

• masculine: этот
• feminine: эта
• neuter: это
• plural: эти

So:

• эта майка = this tank top

Russian usually omits the verb to be in the present tense.

So:

• Эта майка из хлопка literally looks like This tank top from cotton
• but it means This tank top is made of cotton

This is very normal in Russian. In the present tense, есть is usually not used in sentences like this.

Because the preposition из normally takes the genitive case when it means made of / from / out of.

Base forms:

• хлопок = cotton
• шёлк = silk

After из, they become:

• из хлопка
• из шёлка

So the pattern is:

• из + genitive = made of / from

Yes, absolutely.

Both are natural:

• майка из хлопка = a tank top made of cotton
• хлопковая майка = a cotton tank top

The difference is small:

• из хлопка focuses a bit more on the material
• хлопковая is a straightforward adjective description

The same works with silk:

• майка из шёлка
• шёлковая майка

Поэтому means therefore, so, or that’s why.

In this sentence, it links the first idea to the result:

• Эта майка из хлопка, поэтому...
• This tank top is made of cotton, so...

The comma is normal because поэтому connects two parts of the sentence.

Grammatically, yes, ней is the pronoun form from она, and it can mean in her in other contexts. But here it refers to the feminine noun майка, so it means in it.

Russian pronouns follow the grammatical gender of the noun:

• майка is feminine
• so the pronoun is feminine too: она, её, ей, ней, etc.

So:

• в ней = in it / while wearing it

Ней is the form of она used after a preposition here.

With в, you get:

• в ней

A useful thing to notice: after many prepositions, Russian third-person pronouns often gain an initial н:

• она → в ней
• он → в нём
• они → в них

So this is a very common pattern.

Because Russian often expresses this idea as it is comfortable in something rather than something is comfortable.

So:

• в ней удобно = it is comfortable in it / it is comfortable to wear
• в ней удобнее = it is more comfortable in it

This focuses on the experience of wearing the garment.

If you say она удобнее, that can also be correct, but it sounds more like this one is more comfortable as an object being compared.
В ней удобнее is especially natural when talking about how it feels to wear.

It is the comparative form meaning more comfortable.

It comes from удобный / удобно. In this sentence, it works in an impersonal way:

• удобно = comfortable
• удобнее = more comfortable

Compare:

• Мне удобно = I am comfortable
• В этой майке удобно = It is comfortable in this tank top
• В этой майке удобнее = It is more comfortable in this tank top

So here удобнее does not agree with майка in gender or number. It stays the same.

Чем means than in comparisons.

So:

• удобнее, чем... = more comfortable than...

In the full sentence:

• в ней удобнее, чем в майке из шёлка
• more comfortable in it than in a silk tank top

Russian repeats в because the comparison is really between two situations:

• in this cotton tank top
• in a silk tank top

Yes, it could be shortened in some contexts, but the full version is very clear and natural.

Full version:

• чем в майке из шёлка

Possible shorter version:

• чем в шёлковой майке

And sometimes, if the noun is obvious from context, Russian can omit it more easily than English. But for learners, the full phrasing is easier to understand and safest to use.

Yes.

The correct form is:

• шёлк
• шёлка

The letter ё is pronounced yo, so:

• шёлк sounds roughly like shyolk

In many Russian texts, people write е instead of ё, so you may often see:

• шелк
• шелка

But the pronunciation is still шёлк, not шелк with a plain e sound.

Yes. Russian word order is fairly flexible.

The given sentence is natural:

• Эта майка из хлопка, поэтому в ней удобнее, чем в майке из шёлка.

But other word orders are possible depending on emphasis, for example:

• Эта майка из хлопка, поэтому удобнее в ней, чем в майке из шёлка.

The original version sounds smooth and neutral. For a learner, it is a good model to follow.