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Storm Windows

Indow Window Inserts

Laser-measured acrylic panels edged in silicone compression tubing that press into the frame with no hardware. Five grades, a lifetime warranty on the acrylic, 1,500-plus reviews averaging 4.5 stars, and a price to match.

4.6
$20–$36 per sq ft
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Pros

  • Compression tube seals out-of-square old windows with no frame, magnets, or screws
  • Five grades: Standard, Acoustic (1/4 in), Museum (98% UV block), Commercial, Sleep and Shade
  • Published figures: 50% noise cut for Standard, 70% for Acoustic, about 19% heating savings
  • Lifetime warranty on the acrylic, five years on the tubing, Snug Fit guarantee
  • 4.5 stars from more than 1,500 verified reviews; BBB A rating

Cons

  • Priciest DIY insert on the market, and prices rose 10% in July 2026
  • Lead times of weeks to months, especially for Acoustic Grade
  • Noise reduction depends on a 3-to-6-inch air gap the ordering process does not stress
  • Some owners report corner gaps, popping edges, and condensation at the sill

Specifications

MountingPatented silicone compression tube, press-fit
Standard gradeNominal 1/8 in acrylic; drafts and heat
Acoustic gradeNominal 1/4 in acrylic; noise
Museum gradeBlocks 98% of UV
Commercial gradeAbrasion-resistant coating
Noise (over single pane)Standard 50% (10–12 dBA); Acoustic 70% (18.9 dBA)
EnergyAbout 19% average heating cost reduction in a cited field study
PriceAbout $20–$28/sq ft Standard; $25–$36 higher grades; ~$40 Commercial
WarrantyLifetime on acrylic; 5 years on tubing; Snug Fit guarantee
CompanyIndow, Portland, Oregon, founded 2009

Our Verdict

The best interior storm window you can buy without a contractor, and the one to choose for an old house with windows that are not square. Read the air-gap rule before ordering Acoustic Grade, and budget for the wait.

4.6

Overview

Indow, founded in Portland, Oregon in 2009, makes the interior storm window most people picture when they hear the term. Each insert is a sheet of clear acrylic edged in a patented silicone compression tube. The company laser-measures your window opening, cuts the panel to match, including any out-of-square corners, and you press it in. There is no frame, no magnet strip, no screw, and from across the room the insert is nearly invisible.

It is our Best Overall pick in the storm window roundup for that reason. This review looks harder at what it costs, how long it takes, and where the roughly 13 percent of reviewers who do not recommend it ran into trouble.

Grades

  • Standard Grade uses nominal 1/8-inch acrylic and is the pick for drafts and heating bills.
  • Acoustic Grade doubles that to 1/4 inch for noise.
  • Museum Grade blocks 98 percent of UV to protect furnishings and art.
  • Commercial Grade adds an abrasion-resistant coating for high-traffic buildings.
  • Sleep and Shade use opaque or tinted acrylic for bedrooms and glare.

The compression tube

The tube is the product. It squeezes against the inside of the frame to make a seal Indow describes as airtight, and it forgives the racked openings every old house has. Removal is pulling one corner. Installation is seating the bottom edge and pressing up the sides. Our install guide covers the measuring rules; for Indow you send the raw measurements and they do the math.

The tube is also the wear item. It is silicone, warranted for five years against heat, cold, and UV, against a lifetime warranty on the acrylic itself.

Performance

Indow publishes numbers, which most competitors do not. Over single-pane glass, Standard Grade cuts noise about 50 percent (10 to 12 dBA) and Acoustic Grade about 70 percent (18.9 dBA). A field study the company cites found heating costs fell an average of 19 percent after installation. Those are single-pane figures; over double-pane windows the gains are real but smaller.

Owner reviews back the claims with a caveat. On Reviews.io, where Indow has 1,559 verified reviews averaging 4.5 stars and an 87 percent recommendation rate, customers report 6 to 10 decibel reductions and rooms that are "significantly more comfortable." The dissatisfied minority cluster around one issue: noise reduction needs an air gap. A customer with 1 1/2 inches between insert and glass got no acoustic benefit and then learned Indow prefers 3 to 6 inches. The company does not guarantee noise reduction, and a BBB reviewer with Acoustic Grade reported "absolutely no noise reduction" against a neighbor. If your window has a shallow stool, ask before buying Acoustic.

Fit and condensation

Indow offers a Snug Fit guarantee and, per multiple reviewers, honors it, in one case replacing inserts twice until fourteen of them fit. But fit complaints exist: edges that pop out and have to be forced, gaps at corners, and condensation at the bottom of the insert. Condensation between insert and glass means warm room air is getting past the seal; the DOE's fixes are in our install guide. A gap means a measuring error, and Indow's customer service, praised across every review platform we checked, will remake the panel.

Price and lead time

Independent pricing guides put Standard Grade at roughly $20 to $28 per square foot, the Acoustic, Museum, and Shade tiers at $25 to $36, and Commercial near $40. A typical 3-by-4-foot window in Standard lands around $250 to $400. Indow raised prices 10 percent in July 2026, so older quotes run low. Professional measurement and installation adds a few dollars per square foot.

Lead time is the other cost. Inserts are custom-made; one reviewer waited three months for Acoustic Grade. Order in late summer for winter.

Reputation

BBB rates Indow an A with two closed complaints in three years, not accredited. Reviews.io shows 4.5 stars over 1,559 reviews. Trustpilot reviews are fewer and more mixed, with fit and condensation the recurring themes and customer service the recurring praise.

Who should buy it

Anyone with one to a dozen leaky windows who wants the best seal available, does not want hardware on the trim, and can wait for delivery. Historic-home owners especially, since nothing touches the original window. Choose Acoustic Grade only if you have 3 inches or more of gap.

Choose a Window Savers kit if you have fifteen windows and a steady tape measure, or Climate Seal if you want magnetic removal and a stronger acoustic option. The storm window roundup compares all of them.

Sources