Learn Hardcore Swedish: Du kan bli varm snabbare genom att klä på dig en tjock tröja. - You can get warm faster by putting on a thick sweater.

bli varm snabbare = get warm faster (focus on the speed of becoming warm)
bli varmare = become warmer (focus on the degree of warmth, i.e. warmer than before)

Here the sentence talks about how quickly you warm up if you put on a thick sweater, so Swedish prefers snabbare to compare the speed of the process.

You could also say:

Du kan bli varm fortare genom att … (using fortare instead of snabbare, similar meaning)
Du kan bli varm snabbare om du tar på dig en tjock tröja. (using om "if" instead of genom att "by")

But bli varm snabbare is the most natural in this context.

Why do we need kan here? Could we say Du blir varm snabbare instead?

Both are possible, but there’s a nuance:

Du kan bli varm snabbare …
= You can get warm faster …
This talks about a possibility / potential result if you choose to do this.
Du blir varm snabbare …
= You get warm faster …
This sounds more like a general fact or something that reliably happens.

In instructions, advice, or explanations of what you can do to achieve something, Swedish very often uses kan:

Du kan spara pengar genom att … – You can save money by …
Du kan lära dig svenska snabbare genom att … – You can learn Swedish faster by …

So kan fits the advisory/”tip” tone of the sentence.

Why do we say genom att before the verb? What does that construction mean?

Genom att is a very common way to say “by (doing something)” in Swedish.

Structure:

genom att + infinitive
= by + -ing form of the verb

Examples:

Du kan bli varm snabbare genom att klä på dig en tjock tröja.
= You can get warm faster by putting on a thick sweater.
Du lär dig snabbare genom att lyssna mycket.
= You learn faster by listening a lot.
Man kan spara pengar genom att inte äta ute så ofta.
= You can save money by not eating out so often.

After genom, you almost always need att before the verb in this pattern.

Why is there att before klä på dig?

Att is the infinitive marker in Swedish, similar to “to” before a verb in English.

att klä = to dress
att klä på sig = to get dressed / to put clothes on

In the pattern genom att + verb, att is required:

genom att klä på dig … – by putting on …
genom att läsa – by reading
genom att träna – by exercising

Without att, it would be ungrammatical here:

❌ genom klä på dig → wrong
✅ genom att klä på dig → correct

What does klä på dig literally mean, and why do we need dig?

Klä på (sig) is a so‑called particle verb (like an English phrasal verb). It basically means to get dressed / to put clothes on.

klä = to dress
på = on
sig / mig / dig etc. = reflexive pronoun (“oneself”)

For du, the reflexive pronoun is dig:

Jag klär på mig. – I’m getting dressed.
Du klär på dig. – You’re getting dressed.
Han/Hon klär på sig. – He/She is getting dressed.

In the infinitive with a specific person:

Jag vill klä på mig.
Du behöver klä på dig.

If you leave out dig:

klä på en tjock tröja
sounds like you are dressing the sweater (putting something onto the sweater), not yourself. So you need dig to show that you are the one being dressed.

What is the difference between klä på dig and ta på dig?

Both are related to putting clothes on, but there’s a nuance:

klä på dig (en tjock tröja)
= get dressed / put clothes on (can be more general, “dress yourself (in a thick sweater)”)
ta på dig (en tjock tröja)
= put on (a thick sweater)
This focuses a bit more on the action of putting on that specific item.

In this sentence, både work:

Du kan bli varm snabbare genom att klä på dig en tjock tröja.
Du kan bli varm snabbare genom att ta på dig en tjock tröja.

Many Swedes might actually say ta på dig en tjock tröja in everyday speech, but klä på dig is also natural and correct.

Why is it snabbare and not something like mer snabbt?

Swedish usually forms the comparative of many adjectives and adverbs with -are, not with mer:

snabb (fast) → snabbare (faster)
långsam (slow) → långsammare (slower)
billig (cheap) → billigare (cheaper)

snabbare here is an adverb modifying bli varm (it tells us how quickly you become warm).

Using mer snabbt would sound very strange or wrong in this sentence. Native speakers almost always say snabbare.

Is varm an adjective here? Does it change form depending on gender or number?

Yes, varm is an adjective meaning warm.

After bli (to become), adjectives describe the subject:

Du är varm. – You are warm.
Du blir varm. – You get/become warm.

For adjectives, Swedish does have different forms, but in predicate position (after är, bli, etc.), you usually see:

Common/Ett singular:
Tröjan är varm. – The sweater is warm.
Vattnet är varmt. – The water is warm.
Du är varm.
Plural:
Strumporna är varma. – The socks are warm.

With du as subject, you just use varm:

Du kan bli varm snabbare … – You can get warm faster …

So yes, it’s an adjective, and the form varm is what you expect here.

Why is it en tjock tröja and not den tjocka tröjan?

Both are grammatical but have different meanings:

en tjock tröja = a thick sweater (any thick sweater, not specified)
den tjocka tröjan = the thick sweater (a specific one that both speaker and listener know about)

The sentence is giving general advice, not talking about a particular sweater you already mentioned. That’s why the indefinite form is used:

Klä på dig en tjock tröja. – Put on a thick sweater. (any)

If you were talking about a specific one:

Klä på dig den tjocka tröjan som du fick av mormor.
– Put on the thick sweater you got from grandma.

Could the word order be Du kan snabbare bli varm instead of Du kan bli varm snabbare?

Du kan bli varm snabbare is the normal, natural word order.

Du kan snabbare bli varm is not wrong, but it sounds more formal or slightly marked/emphatic, and is much less common in everyday speech.

General rule for sentences like this:

Main structure: [subject] + [verb] + [complement/adjective] + [adverb]
→ Du (subject) kan bli (verb phrase) varm (complement) snabbare (adverb).

So in normal spoken and written Swedish, prefer:

✅ Du kan bli varm snabbare …
rather than:
⚠️ Du kan snabbare bli varm … (grammatical but less natural here).