Walk the flooring aisle at Home Depot and one blue-green roll dominates the underlayment shelf. Sentinel Protect Plus underlayment is the big-box staple that ends up under a huge share of DIY laminate and floating vinyl plank installs, at roughly $30 to $35 for a 100 sq ft roll — about 30 cents per square foot. It earns the shelf space: a polypropylene foam core with an attached moisture film and overlap-and-tape seam system that covers the three jobs an underlayment exists to do. But it is not the right pick under every floor, and its sound numbers deserve a closer read than the packaging invites. Here is the full review from someone who has rolled out a lot of it.
What It Is and What It Costs
Sentinel Protect Plus is a 2 mm (roughly 5/64″) cross-linked polypropylene foam underlayment with a factory-attached vapor film, sold primarily in 100 sq ft rolls (about 44″ wide by 27.3 ft long) with a 3
-inch film overhang on one edge and adhesive strip for seaming. The roll weighs about 6 lb — one hand carries it up the stairs. At $0.30–$0.35/sq ft it sits squarely mid-market: double the price of bargain 6-mil-poly-plus-basic-foam combos, half to a third the price of premium rubber or heavy felt underlayments like QuietWalk Plus ($0.60–$0.70) or rubber sheets ($0.80–$1.20). It is designed for floating floors only — laminate and click-lock luxury vinyl plank — over wood or concrete subfloors, on, above, or below grade. It is not for glue-down or nail-down floors, and not for under tile.
The Three Jobs It Does
1. Moisture protection
The attached film functions as the vapor retarder that laminate and many LVP manufacturers require over concrete. Sealed at the seams with the built-in overlap and tape strip, it forms a continuous barrier so you skip the separate 6-mil poly sheet — one layer instead of two, and no poly sliding around underfoot as you work. Real-world caveat: a film this thin protects against normal slab vapor, not active moisture problems. On any concrete slab, do the calcium-chloride or RH test first (most flooring specs cap at 5–8 lb MVER or 75–80 percent RH); a wet slab needs an epoxy moisture mitigation coating, not any roll-out underlayment.
2. Sound reduction
The advertised laboratory numbers are IIC 65 and STC 66, and this is where marketing needs translation. Those ratings come from a full floor-ceiling assembly test — typically a 6″ concrete slab with a suspended ceiling below — so most of the number belongs to the concrete, not the foam. Every underlayment brand plays the same game, so treat the figures as comparable within the genre rather than as a promise your bedroom floor will hit IIC 65 over 2×10 joists. What the 2 mm foam genuinely delivers: it kills the hollow clack of laminate walked on in hard shoes, takes the drum-echo out of floating floors, and satisfies typical condo/HOA minimum ratings on concrete-slab buildings (get your building’s spec in writing and check the letter against Sentinel’s test report — most HOAs want the lab assembly cited). If real impact-noise control for a room below is the mission, step up to a 5–6 mm felt or rubber product; physics favors mass, and 2 mm of foam has little.
3. Subfloor smoothing and feel
Two millimeters of cross-linked foam bridges the minor grit, paint drips, and 1/16″-class imperfections of a decent subfloor and gives the floating floor a slightly cushioned, quieter feel. It does not fix real flatness problems — the industry flatness spec (typically 3/16″ in 10 ft) still has to be met with a grinder or leveling compound. Foam that is too thick or soft causes click-joint flex and failure, which is exactly why laminate makers cap underlayment around 3 mm; Sentinel’s 2 mm sits safely inside every major manufacturer’s allowance, including floors whose warranties void over squishy substrates.
Installation: 20 Minutes of Technique
This is genuinely one of the easiest underlayments to install well:
- Sweep and vacuum the subfloor; drive any proud fasteners; verify flatness with a straightedge.
- Roll out the first run film side down on wood subfloors per current instructions — but check the printed instructions in your roll; the operative rule across brands is simply to keep the film continuous and the seams sealed. Run the length of the room in the same direction you will lay the planks, or perpendicular — direction does not affect performance; running perpendicular to the plank direction avoids having a foam seam and a plank seam stack on top of each other, which is the tidier practice.
- Butt the foam edges — never overlap the foam itself (a doubled 4 mm ridge telegraphs through laminate as a bouncy line). Lap only the film flap from the adjacent run over the neighboring sheet and stick it down with the integrated adhesive strip; tape any cut seams and perimeter gaps at pipe penetrations with sheathing or underlayment tape.
- Trim with a utility knife against the wall, run the film slightly up the wall on concrete installs (the baseboard hides it), and lay flooring the same day — foot traffic and dropped tools chew up exposed foam.
Only install what you will floor over in a session, and stagger your body weight on the subfloor, not the fresh foam, as you work rows. One roll covers 100 sq ft with effectively zero waste since offcuts patch closets and alcoves.
Versus Cork and Rubber, Briefly
Full reviews of the competing categories live in their own articles; the placement summary is this. Cork (typically 6 mm, $0.50–$0.75/sq ft) offers better genuine impact isolation and thermal comfort but needs a separate vapor barrier on concrete, costs double, and hates moisture. Rubber ($0.80–$1.20) is the performance king for sound and durability, common under engineered wood in high-end condo work, and overkill under a $2.50/sq ft laminate. Felt-fiber hybrids like QuietWalk Plus split the difference with more mass than foam and an attached barrier. Sentinel Protect Plus wins its lane on price-per-performance simplicity: barrier included, seams engineered, weight negligible, and thickness compliant with every click floor on the same store’s shelves. Note too that a large share of mid-range LVP now ships with pre-attached pad — under those floors, adding Sentinel is usually prohibited by the flooring warranty except as a film-only vapor layer, so check the plank box before buying rolls.
Mistakes That Show Up a Year Later
Underlayment failures are quiet and delayed, so learn the patterns before laying plank one. Overlapped foam seams announce themselves months later as a soft ridge line where click joints flex and eventually pop — butt the foam, lap only the film. Unsealed seams over concrete let slab vapor bypass the barrier and cup laminate near the middle of the room, a failure invariably blamed on the flooring brand. Doubling underlayment “for extra softness” under pad-attached LVP is the most common warranty-voiding move in DIY flooring; if the plank has pad, the only thing you may add on concrete is a film-class vapor barrier, and the plank maker’s instructions govern. Finally, skipping the flatness check because the foam “will even it out” guarantees clicking noises at every dip deeper than the foam’s 2 mm — the underlayment smooths texture, never topography. Ten extra minutes with a straightedge and a roll of seam tape prevents essentially every callback this product ever generates.
Verdict
Rated against what it costs and what floating floors actually need, Sentinel Protect Plus underlayment is an easy recommendation for the mainstream case: laminate or click LVP, residential rooms, sane subfloor, concrete or plywood underneath. You get code-and-warranty-satisfying vapor protection, legitimate hollow-sound damping, and the fastest seam system in the aisle for about $30 a room. Spend more only when a downstairs neighbor or an HOA acoustic spec is the driving problem — that is rubber-and-felt territory — and spend less on nothing: the $12 bargain rolls with flimsy films are where floating-floor moisture claims come from. As big-box staples go, this one is a staple for the right reasons.
