Underlayment is mostly not waterproof. It is moisture-resistant. This thin layer under flooring helps with sound, comfort, and leveling. It mostly stops water vapor, not liquid water.
I have worked with underlayments for many years. I have seen how they perform in many settings. Many people think underlayment makes a floor fully waterproof. This is not true for most types. Underlayment creates a barrier against moisture. This helps protect the flooring above it. It stops vapor from moving up from the subfloor. Knowing this difference helps you pick the right product for your needs.
![Underlayment moisture barrier protection](https://meettfit.com/wp-content/uploads/2025/07/33f1acb4-76f3-40a9-b488-c1ca57acbdd11.png")
Let’s look closer at what underlayment does.
What is Underlayment?
Underlayment is a thin layer of material. It goes between the subfloor and the finished flooring.
Underlayment serves many purposes. It adds cushioning underfoot. It also helps reduce sound. It can even out small bumps in the subfloor. Most importantly, it can act as a moisture barrier. This protects your flooring from humidity. Without the right underlayment, your flooring might not last as long. Unchecked moisture can lead to serious problems like warping, cupping, mold growth, or even structural damage to your flooring materials.
Types of Underlayment
- Schuim: Often used for laminate and engineered wood. It adds comfort and sound dampening.
- Felt: Good for sound control. It is also a good insulator.
- Kurk: Natural and eco-friendly. It offers great sound dampening and insulation.
- Rubber: Very durable and good for high-traffic areas. It has excellent sound and shock absorption.
- Composite: Made from blends of materials. It offers combined benefits like moisture resistance and sound proofing.
![Different types of flooring underlayment](https://meettfit.com/wp-content/uploads/2025/07/086e1617-2bf9-4a4e-8ab5-8b5b243ad5381.png")
Now, let’s talk about underlayment and water.
Is Underlayment "Waterproof"? The Core Answer!
Most underlayment is not truly "waterproof." It is "moisture-resistant" or "water-resistant."
This is a key point I always make to clients. Waterdicht means it completely stops liquid water. It will block water even if it sits on the surface for a long time. Moisture-resistant means it slows down or stops water vapor. It does not stop liquid water from soaking through if there is a flood. Think of it like this: a rain jacket is waterproof. A windbreaker is water-resistant. The main goal of most underlayments in terms of water is to prevent moisture vapor from the subfloor from damaging the finished floor. If excess moisture vapor from sources like concrete slabs, damp crawl spaces, or high ambient humidity reaches your flooring, it can cause problems like swelling, delamination, buckling, or the growth of mildew and mold. These issues can degrade your flooring’s appearance and lifespan.
Moisture Barrier vs. Waterproof
- Vochtbarrière: This stops water vapor from getting through. It does not stop liquid water if it pools.
- Waterproof: This completely blocks liquid water from passing. It keeps the area dry even with long water contact.
Underlayments get "moisture-resistant" in two ways. Some materials, like closed-cell foam, are naturally resistant. Other underlayments have an added layer. This is often a polyethylene film. This film helps block moisture. Common moisture-resistant underlayments include foam with a film. Also, rubber or cork can have good moisture properties. For areas truly prone to standing water or frequent spills, like bathrooms, laundry rooms, or basements, a dedicated waterproof membrane is often needed in addition to of instead of a standard underlayment, especially under tile. These membranes form a continuous, impermeable barrier against liquid water.
![Understanding moisture barrier vs waterproof](https://meettfit.com/wp-content/uploads/2025/07/921e91c6-ca76-4e1a-9ad8-263a9c361dac1.png")
The floor type also matters for underlayment choice.
Different Flooring Types and Underlayment Water Needs
Different flooring types need different underlayment properties. This is true for moisture control too.
Laminaatvloeren
Laminate floors need moisture protection. This stops swelling and mold of the fiberboard core. Some laminate flooring has a pad attached. Even then, you might need more underlayment. This depends on your subfloor and moisture levels. My experience shows that an extra layer often helps, especially to prevent the edges of the planks from peaking or cupping due to moisture absorption.
Hardwood Flooring
Moisture hurts hardwood floors significantly, leading to cupping, crowning, gapping, or warping. Underlayment for hardwood helps with moisture, sound, and comfort. In wet places, like a basement, choose an underlayment with a strong moisture barrier. This is critical for hardwood longevity and stability.
Vinyl Flooring / LVP/LVT
Vinyl floors are usually water-resistant themselves. Underlayment for vinyl focuses on leveling, sound, and feel. In wet areas like bathrooms, a moisture-resistant underlayment can still add a layer of protection. This is good even if the vinyl is waterproof, providing an extra safeguard against any subfloor moisture.
Tile
Underlayment for tile, like cement board, gives a stable base. It helps stop cracks. It does not mostly waterproof the floor. Waterproofing for tile comes from waterproof membranes or grout. These are put on top of the underlayment, especially in shower areas or wet rooms, to create a fully impermeable system against liquid water.
Tapijt
Underlayment for carpet mainly gives cushion, sound dampening, and warmth. Water resistance is not the main point. But, a moisture barrier can stop mold from growing under the carpet. This is especially true in damp areas like basements, preventing musty odors and potential health issues.
![Underlayment needs for different flooring](https://meettfit.com/wp-content/uploads/2025/07/94f19ba2-7a9c-42f0-b552-52773de093291.png")
Choosing the right underlayment is important.
How to Pick the Right Underlayment for Best Moisture/Water Protection?
Picking the right underlayment is key. It makes sure your floor lasts and performs well.
Evaluate Environment Humidity
The moisture level of where you install is the main thing to consider. A damp basement needs different underlayment than a dry living room. I always tell clients to measure humidity levels first, often using a hygrometer or moisture meter for the subfloor.
Consider Flooring Type
As I said, different floors have different needs. Match the underlayment to your flooring material. This ensures best performance and protection. Also, consider your subfloor material; concrete slabs are notorious for emitting moisture vapor, requiring a robust moisture barrier.
Product Labels and Certifications
Look for labels that show moisture ratings or waterproof claims. Trust certified products. These labels tell you the product’s true ability to handle moisture. For moisture barriers, look for their Perm Rating, which indicates how much water vapor can pass through the material. A lower perm rating means better moisture resistance.
Integrated Moisture Barrier
Some underlayments come with a moisture barrier already attached. This can save time and effort. It also ensures proper installation of the barrier.
Professional Advice
If you are unsure, ask a flooring expert. They can help you choose the best underlayment for your specific project. I often help clients with this choice, evaluating both the flooring and environmental factors to recommend the optimal solution.
![Choosing the best underlayment for moisture](https://meettfit.com/wp-content/uploads/2025/07/1ec1504b-01b2-43d3-9c40-2cc579515e0b1.png")
Proper installation is also very important for moisture control.
Underlayment Installation Tips (for Moisture/Water)
Good installation makes sure your underlayment works right. This is true for moisture protection too.
Voorbereiding van de ondervloer
Make sure your subfloor is clean, dry, and flat. Any bumps or moisture can hurt the underlayment’s performance. It can also damage the finished floor. Address any existing leaks or excessive moisture sources before installation.
Moisture Barrier Overlap
If you use a separate moisture barrier or an underlayment with one, make sure to overlap the seams. Then, tape them tightly with approved moisture-resistant tape. This creates a continuous barrier against moisture.
Edge Treatment
Handle edges near walls and posts carefully. Seal these areas to prevent moisture leaks. This helps keep the entire floor protected. Ensure the moisture barrier extends slightly up the walls (often called a "bathtub" effect) to redirect any wall-seeping moisture.
Ventilatie
Keep the area well-ventilated during and after install. Good airflow helps moisture escape. This stops buildup that can harm your floor. Consider using dehumidifiers in particularly damp environments to maintain ideal humidity levels.
Conclusie
Most underlayment offers moisture resistance, not full waterproofing. It protects against vapor, extending your floor’s life. Choose based on floor type and environment, considering the perm rating and ensuring correct installation.
Ready to find the perfect underlayment solution for your project? Contact my team today for a custom quote or to request a free sample. We are here to help optimize your design and ensure the best performance for your product.