Το υπόστρωμα κρατάει υγρασία.

• Το = the
• υπόστρωμα = substrate, base layer, underlayer, depending on context
• κρατάει = holds, retains, keeps
• υγρασία = moisture, humidity, depending on context

So the sentence is built very literally as The substrate holds moisture.

Because υπόστρωμα is a neuter noun in Greek.

Greek nouns have grammatical gender:

• ο for masculine
• η for feminine
• το for neuter

So:

• το υπόστρωμα = the substrate

A useful clue is that many neuter nouns end in -μα, and υπόστρωμα is one of them.

It is in the nominative case, because it is the subject of the sentence — the thing doing the action.

Here:

• το υπόστρωμα = the subject
• κρατάει = the verb
• υγρασία = the object

With many neuter nouns, the nominative and accusative forms are the same, so the form υπόστρωμα does not change here.

κρατάει is the 3rd person singular present tense form of κρατάω / κρατώ, meaning to hold, to keep, to retain.

So κρατάει means:

• he/she/it holds
• it keeps
• it retains

In this sentence, the subject is το υπόστρωμα (it), so κρατάει = it holds / it retains.

Yes. In modern Greek, both κρατάει and κρατά are common and correct.

So these are both fine:

• Το υπόστρωμα κρατάει υγρασία.
• Το υπόστρωμα κρατά υγρασία.

The meaning is the same.
Very generally:

• κρατάει can sound a little fuller or more everyday in some contexts
• κρατά can sound slightly more concise

But in normal speech and writing, both are standard.

Because Greek often leaves out the article when speaking about something in a general or non-specific way.

So:

• κρατάει υγρασία = retains moisture / holds moisture in general
• κρατάει την υγρασία would sound more like retains the moisture, referring to a more specific moisture already understood from context

This is similar to English:

• Plants need water
• The plants need the water we collected yesterday

So here, υγρασία is being used in a general sense.

It is in the accusative case, because it is the direct object of the verb κρατάει.

The sentence structure is:

• Το υπόστρωμα = subject
• κρατάει = verb
• υγρασία = direct object

For feminine nouns like υγρασία, the accusative singular often looks the same as the nominative when there is no article in front of it, so the role is understood mainly from sentence structure.

If you added the article, you could see the case more clearly:

• η υγρασία = nominative
• την υγρασία = accusative

υπόστρωμα is pronounced roughly as:

ee-PO-stro-ma

The stress falls on πό:

• υπόστρωμα

The written accent mark in Greek shows which syllable is stressed. Stress is important in Greek pronunciation, so learners should pay close attention to it.

The whole sentence is roughly pronounced: to ee-PO-stro-ma kra-TA-ee ee-gra-SEE-a

This is only an approximation using English letters, but it helps locate the stress:

• υπόστρωμα
• κρατάει
• υγρασία

It can mean either, depending on context.

• υγρασία often means moisture when talking about materials, soil, surfaces, etc.
• It can also mean humidity when talking about the air or weather

In Το υπόστρωμα κρατάει υγρασία, moisture is the most natural translation, because a substrate or base material is something that can retain water content.

Yes, Greek word order is more flexible than English word order.

The neutral, straightforward order here is:

• Το υπόστρωμα κρατάει υγρασία.

But other orders are possible for emphasis, for example:

• Υγρασία κρατάει το υπόστρωμα.
  This would usually sound marked or unusual, and could even be confusing without context.
• Κρατάει υγρασία το υπόστρωμα.
  This can work if you want to emphasize what the substrate does

In most cases, for a learner, the basic subject + verb + object order is the safest choice.

It can mean either, and context decides.

In this sentence, it most naturally expresses a general property or habitual fact:

• The substrate retains moisture

Greek present tense often covers both:

• it is holding
• it holds
• it tends to hold

So κρατάει here does not necessarily mean the substrate is actively doing it at this exact second. It usually means this is one of its normal characteristics.

It is more like retain in this context.

The verb κρατάω / κρατώ is very common and can mean different kinds of holding:

• physically holding something in your hand
• keeping something
• retaining something
• lasting or enduring in some contexts

In Το υπόστρωμα κρατάει υγρασία, it means the material keeps moisture inside it or retains moisture. So while the basic idea is hold, the best English choice is often retain.

Yes. A more formal or technical option might be:

Το υπόστρωμα διατηρεί υγρασία.

Here, διατηρεί means maintains or retains.

The difference is mainly one of style:

• κρατάει υγρασία = very natural, common, everyday
• διατηρεί υγρασία = a bit more formal or technical

Both are correct, but κρατάει is perfectly normal and widely used.