For SPC and LVT specifiers, underlayment often gets overlooked—at least until no...
For SPC and LVT specifiers, underlayment often gets overlooked—at least until noise complaints start piling up, or click-lock seams begin to gap a couple years in. Most of the time, these problems come down to one thing: IXPE or EVA. Both foams seem similar on the roll, but their performance over time—especially with sound, compression, and moisture—couldn't be more different.
This guide takes a close look at IXPE and EVA underlayment, comparing real performance: IIC, STC, Delta IIC, compression set, water vapor transmission, and service temperature. There's also a checklist for private-label SPC and LVT buyers, so you can match the right material to your project's risk before you order.
The big difference is in compression set and Delta IIC: IXPE keeps 75–85% of its thickness after ten years, showing a compression set of 15–25% (ASTM D3575). EVA loses 1–2 mm of thickness, with a 40–60% compression set, often pushing click-lock seams past the ±0.3 mm tolerance and causing separation. If you want a floor to meet acoustic codes and warranty terms for its full lifespan, you need to look past upfront price or instant compression strength and focus on these numbers.
IXPE is an irradiated cross-linked polyethylene foam with a tight, closed-cell structure. EVA is a chemically foamed ethylene-vinyl acetate copolymer with a less uniform cell network. The material you pick affects sound, compression, moisture resistance, and how many claims you'll see after ten years.
IXPE (irradiated cross-linked polyethylene) is made by exposing polyethylene sheets to electron beams, which create bonds between the polymer chains. Then, physical foaming (not chemical blowing agents) expands the structure, forming a tight closed-cell honeycomb. The result is an IXPE pad with over 95% closed cells and a density of 33–90 kg/m³ (ASTM D1622). This dense cell structure blocks water and helps the foam keep its shape, even under heavy loads.
EVA (ethylene-vinyl acetate) uses chemical foaming. Blowing agents like ADC or AZ mix with the polymer, and heat breaks them down, releasing gas that makes the foam. This method gives EVA a closed-cell ratio of 80–90% and density of 100–110 kg/m³. The higher density is partly because of leftover polymer and some incomplete cell formation. EVA foam can have leftover chemicals that might off-gas when heated. Chemical foaming costs less than electron-beam cross-linking, but it doesn't create as even a cell structure as IXPE.
IXPE usually does better than EVA for sound insulation, thanks to its uniform closed cells. At 3 mm, IXPE generally gets IIC 75–78 and STC 73–77. EVA, at the same thickness, gets IIC 68–72 and STC 65–70. Delta IIC (ASTM E2179) is the best way to compare, since it isolates the underlayment's effect.
ASTM E2179 measures what the underlayment actually adds, not the whole floor assembly. IXPE at 3 mm gives Delta IIC 18–22, while EVA at 3 mm gives Delta IIC 10–14. Always ask for Delta IIC numbers when comparing products. Otherwise, IIC claims can be all over the place, depending on the slab, joists, or ceiling used in the test. Without Delta IIC, you can't really trust the noise ratings.
Lab IIC (ASTM E492-09) happens in perfect test rooms, but field FIIC (ASTM E1007) measures real installations—with seams, HVAC holes, and uneven subfloors. Field scores usually drop 3–5 points below the lab. So, if you need FIIC ≥ 70, you should specify lab IIC ≥ 75 to have a safety margin. Basically, add 5 points to your field target when you write specs, so your floor meets acoustic rules even after installation quirks.
Compression set is the permanent thickness loss after a foam is loaded for a long time, checked by ASTM D3575 at 22 hours and 70°C. IXPE usually stays at 15–25% compression set; EVA goes up to 40–60%. This number, not just how strong the foam feels at first, tells you if a click-lock system will start to gap after a few years.
Compression strength (CS) shows how much force the foam can take in the moment, measured in kPa (EN 826). EVA scores about 105 kPa, IXPE about 90–95 kPa. Some buyers think higher CS means longer life, but that's not true. CS is just the instant reaction. Compression set (ASTM D3575 Suffix B / ISO 1856) shows what stays compressed after 22 hours at 70°C. IXPE bounces back, losing only 15–25% thickness, while EVA stays squished, losing 40–60%. Click-lock floors can only handle a ±0.3 mm change; more than that, seams gap and you get warranty claims in a few years.
IXPE underlayment tested by ASTM D3575 shows 15–25% compression set, meaning less than 0.5 mm thickness loss over 5–10 years, even with regular traffic or heavy furniture up to 30 kg. EVA, at 40–60% compression set, loses 1–2 mm under the same use, which blows past the ±0.3 mm click-lock limit and causes visible gaps. High-grade IXPE stays stable even on radiant-heat floors (up to 45°C), but EVA's cells collapse faster and can release leftover chemicals when heated up and cooled down repeatedly.
IXPE blocks moisture better, with a water vapor transmission rate (ASTM E96) under 1.0 g/m²/day. EVA lets through 3–5 g/m²/day. IXPE handles radiant heat up to 80°C, while EVA starts to soften above 60°C. The density difference is just from how they're made, not a sign of better performance.
IXPE's closed-cell ratio is over 95%, so its honeycomb structure really stops moisture from getting through. EVA only gets 80–90% closed cells, so some water can sneak past. Water vapor transmission rate (ASTM E96) tells you how much moisture moves through each day: IXPE stays at or below 1.0 g/(m²·day), EVA lets through 3–5 g/(m²·day). For concrete or basement installs, you need that lower IXPE rate to avoid mold or glue failure under the floor.
IXPE stays solid at up to 80°C, and can handle short bursts up to 100°C without losing shape. EVA tops out at 60°C; above that, it softens, cells puff up, and leftover chemicals can turn into VOCs. Radiant heat systems usually keep the surface at 27–29°C, but underneath, the slab can hit 45°C. EVA over radiant heat will compress faster and may start to smell. IXPE stays stable and keeps indoor air safe, even with heat cycling.
IXPE gives you better longevity, sound reduction, and moisture resistance, and works with radiant heat, but costs 20–30% more than EVA and feels softer underfoot. EVA wins on upfront price and is good for quick projects or rentals, but it compresses faster, lets in more moisture, and can give off odors from leftover chemicals.
Pros:
● Compression set (ASTM D3575) of 15–25% means the pad keeps its thickness for 10+ years, stopping click-lock seams from opening.
● Delta IIC (ASTM E2179) of 18–22 at 3 mm meets field FIIC ≥ 70 for multi-family buildings.
● Water vapor transmission rate (ASTM E96) ≤ 1.0 g/(m²·day) keeps out moisture from concrete or basements.
● Works up to 80°C, so it's safe for radiant heat systems.
● FloorScore and GREENGUARD Gold certified for low VOCs—good for schools and hospitals.
Cons:
● Costs 20–30% more than EVA, which can squeeze margins on budget products.
● Softer feel underfoot, which some buyers might not like if they want a firmer floor.
● Electron-beam cross-linking needs special equipment, so not every supplier can make it, and lead times can be longer.
Pros:
● Cheapest per-square-foot, so it's often picked for rentals or short-term projects.
● Compression strength (EN 826) of about 105 kPa gives a firm, springy feel at first.
● Chemical foaming and simple tooling make it easy and fast to produce.
Cons:
● Compression set of 40–60% means it loses 1–2 mm in 5–10 years, breaking the click-lock limit and leading to warranty headaches.
● Delta IIC of 10–14 isn't enough for condos or projects needing real sound control.
● WVTR of 3–5 g/(m²·day) lets moisture in, risking mold in basements or on concrete.
● Only good to 60°C, so you can't use it with radiant heat, and heat cycles can release more VOCs from leftover chemicals.
Pick IXPE if you’re working on multi-family homes, hospitals, hotels, or anywhere with radiant heating or damp subfloors. EVA fits better for short-term, budget projects that don’t have heated floors. For private-label SPC/LVT, check that peel strength is at least 1.5 N/mm and ask for third-party test reports before you sign with a supplier.
IXPE really shines in apartment buildings where the field-tested IIC (FIIC) needs to hit 70 or higher. Condo rules or city codes often ask for that. Hospitals, schools, and hotels that want FloorScore or GREENGUARD Gold certification should go with IXPE—it helps avoid off-gassing problems, especially when the floor heats up and cools down. For radiant heating, IXPE just holds up better. It handles service temps up to 80°C, while EVA starts to break down above 60°C and can give off VOCs. Basements and damp spaces do better with IXPE too, since its water vapor transmission rate (WVTR) is 1.0 g/(m²·day) or less (ASTM E96), while EVA sits around 3–5 g/(m²·day). In stores with rolling carts or heavy loads over 25 kg, IXPE’s 15–25% compression set (ASTM D3575) helps prevent the floor from getting squished and the click-lock system from failing over the years.
EVA works for single-story houses where there’s no one living below and you don’t need high sound ratings—Delta IIC of 10 is enough in those cases. For rentals or leases with less than three years between tenants, EVA helps keep costs down, as long as the subfloor is dry and above ground. Entry-level SPC sold at low prices often uses EVA to stay competitive, but it’s important to be upfront about the specs. If compression set goes over 40% after 22 hours at 70°C (ISO 1856), that can cause warranty headaches. Low-traffic spots like guest rooms, closets, or storage can handle EVA’s 40–60% compression set. The click-lock system, with a tolerance of ±0.3 mm, usually holds up fine there since there’s not much weight on it.
Manufacturers bond attached IXPE underlayment (1–1.5 mm) to the SPC core with PUR or EVA hot-melt adhesives. It needs a peel strength of at least 1.5 N/mm (GB/T 2790 or ASTM D903). For loose-laid IXPE (2–5 mm), you just float it with a 4-inch overlap sealed by vapor tape—no glue needed.
Not always. IXPE at 2 mm gives Delta IIC 16–18 (ASTM E2179), 3 mm gets 18–22, and 5 mm reaches 22–24. The improvement slows down after 3 mm. If you go thicker, double-check the SPC floor’s click-lock height tolerance or you might get seam separation.
EVA copolymer itself isn’t toxic. But leftover chemicals from ADC or AZ blowing agents can off-gas, especially when heated. Good-quality EVA underlayment keeps TVOC under 100 µg/m³ and should have FloorScore certification before you use it for SPC flooring.
IXPE handles 30 kg static loads with less than 0.5 mm thickness loss per year. For point loads above 80 kg, like medical carts, you’ll need high-density IXPE or even XPS. EVA isn’t great for loads over 25 kg since its compression set can drift to 40–60% (ASTM D3575).
IXPE underlayment usually comes with a 15–25 year warranty for homes and 7–10 years for businesses. EVA underlayment tends to offer 5–10 years. If the underlayment fails, it often causes problems with the SPC floor's click-system warranty too. So, matching warranties matters a lot when you're choosing what to use.
