Short answer: for one enclosure door, fit a die-cut or pressed-in gasket and compress it to 25-35 % of its 3-6 mm free height. The continuous foam bead on a factory door comes out of metered dispensing equipment, not a tube. Pumps hold the two-part polyurethane at a fixed mix ratio, and a tracer lays the bead at a set speed, which is why it seals. A hand-applied bead on a single door swings in height along its length, and every thin spot leaks at the first rinse. A profile gasket gives you a gap you have measured, a splice you can place at the top, and a seal you can test with a strip of paper. Here is the sizing, the fit and the checks.
Why the foam-in-place bead is factory equipment
The material is real: a two-part polyurethane that foams, skins over and bonds to the door as one continuous bead. Production cells meter the isocyanate and polyol sides with pumps, mix them in a small static mixer and trace the door at a controlled speed. Formulators grade the foam by density and hardness, the same way silicone cord is graded. It also cures faster in a hot plant than in a cold one, so the working window shifts with the season.
What one door cannot copy is the metering. Hand-mixed foam rises unevenly, and a caulking gun lays a bead whose height follows trigger speed and the shrinking pot life. The over-compressed stretches take a set; the thin stretches leak. By the time you notice, the skin has cured, and the repair means scraping foam off a brushed stainless door.
If you still want to try two-part polyurethane, handle the uncured isocyanate side with nitrile gloves and good ventilation, and follow that product's safety data sheet.
If the real question is a foam strip against a solid profile, the foam-versus-rubber door seal comparison settles it for a sealed door: a solid or dense cellular profile outlasts an open-cell foam strip.
What to order for a single door
Three gasket forms suit a one-off door:
- Die-cut flat gasket — 1.5-3 mm cellular polyurethane or sponge silicone, cut to the door outline with the fastener holes. Suits a flat flange.
- Extruded cord — 3-6 mm cellular polyurethane or silicone cord, pressed into a flange channel or taped to a flat flange, joined with mitred or butt splices.
- Molded corners plus straight cord — factory corners at the four angles and field-cut straights between them, which moves the joints off the corners.
The material follows the environment, not the door (ranges as gasket handbooks publish them; a named profile's datasheet wins):
| Material | Service range | Reach for it when |
|---|---|---|
| Silicone | −60 to 200 °C | Hot washdown and cold outdoor sites; weak against hot caustic and abrasion |
| EPDM | −50 to 150 °C | Hot water, steam and caustic; the washdown default |
| Neoprene | −40 to 120 °C | Oil splash and weathering |
| Nitrile | −30 to 120 °C | Oils and fuels on a dry indoor panel |
Whatever the material, size for 25-35 % compression of the free height. Gasket datasheets put the floor near 20 %, below which flange waviness loses contact, and the ceiling near 50 %, where cellular foam starts to take a permanent set.
If the door itself is the problem — a warped panel or a worn hinge — a custom enclosure built to your size and material beats another round of re-sealing. Adding a gland or a window to that door while you are at it starts at the custom stainless cutouts page.
Sizing the cord for a 24 x 20 in door with a 4 mm gap
Worked example, with example dimensions you replace with your own door's:
- Door outline: 24 × 20 in [610 × 508 mm], a typical wall-mount box door.
- Latched gap, feeler-gauged at the hinge, the latch and two mid-points: 4 mm.
- Candidate gasket: 6 mm cellular polyurethane cord, call it 1/4 in.
- Compression band: 25-35 % of free height.
The rule in words: compression equals free height minus closed height, divided by free height, where the closed height is the latched gap the cord has to fill.
- Compression: (6 − 4) ÷ 6 = 0.33, so 33 % — inside the 25-35 % band.
- Cross-check: cord ÷ gap = 1.5, and a cord about 1.5 times the gap always lands near 33 %.
- Length: 2 × (24 in + 20 in) = 88 in [2235 mm] of cord, plus 1 in [25 mm] for the splice; round up to an 8 ft [2.5 m] length.
The decision: this cord suits latched gaps from 3.9 mm to 4.5 mm (0.65 and 0.75 times its free height). A 2 mm gap takes a 3 mm cord and lands at (3 − 2) ÷ 3 = 33 % again. Above a 4.5 mm gap, order a die-cut profile cut to the measured gap instead of stacking two cords, and hold every point of the door between 25 % and 35 % compression.
Fitting the gasket, step by step
An old flattened seal comes out first; the foam rope replacement guide covers the clean-up without gouging the stainless.
- Close the door and measure the gap with feeler gauges at the hinge, the latch and two mid-points. Write down the smallest and the largest.
- Pick a cord about 1.5 times the average gap, staying inside the 3-6 mm range.
- Dry-lay the cord around the flange from top centre, mitring 45° at each corner, and keep it clear of fastener holes and the hinge line.
- Wipe the flange with isopropyl alcohol on a lint-free cloth and let it flash off.
- Press the cord into the retainer channel where the flange has one; on a flat flange, hold it with a continuous strip of gasket tape. Cut the splice ends square, butt them at top centre and bridge the joint with a drop of silicone adhesive — the spliced-versus-molded gaskets article shows why a poor joint is the first leak.
- Close and latch the door for 24 h so the cord settles into its compressed shape before you test anything.
Checks before you call the seal done
- Paper test. Close the door on a 25 mm wide paper strip laid against the gasket and pull. Even drag around the loop means contact everywhere; a strip that slides out freely marks under 20 % compression, usually at the splice.
- Latch feel. The door should latch with the same effort as before. Corners standing proud or a latch that needs a shove point at over-compression.
- Water check. After the 24 h settle, rinse the door with a hose. A dry flange line behind the gasket is what a Type 4 door is built to deliver, since Type 4 covers hose-directed water and washdown.
The gasket, the door and the hinges are part of what the maker rated; these boxes are rated NEMA 4X / IP66 by the manufacturer, not UL listed. What a NEMA 4 rating asks of gaskets, doors and hinges lists the other parts the rating leans on, and the NEMA enclosure types guide sorts out which type your site calls for.
Mistakes that cost the seal and the rating
- Cord too small for the gap. Below 20 % compression the seal leaks across flange waviness; remeasure and step up a size.
- Cord too big. Above 50 % the foam takes a set in its first season and the corners stand proud; step down or order a taller die-cut profile.
- Splice at a bottom corner. Water sits there and wicks through the joint; the splice belongs at top centre.
- Adhesive across the compression face. The glue line holds the cord off the flange; adhesive goes on the butt joint only.
- A screw or stud through the cord line. It compresses that point to zero and starts the drip line.
- Reusing flattened foam. An old cord that now measures 4 mm free height will never return to its original height; replace it.
A re-sealed door keeps its rating only when the profile and the door hardware match what the drawing specified; what a panel keeps after you cut it and mount devices sorts the rest of the rating after modifications.
Catalog dimensions to compare
Compare these catalog dimensions with your component layout. Open each enclosure for its rating, material and usable space, then check those specifications against your application.
| Enclosure | Material | Outside H x W x D / display | Rating |
|---|---|---|---|
| 12 × 10 × 6 in | 304 stainless | 12 x 10 x 6 in | Rated NEMA 4X / IP66 by the manufacturer; not UL listed |
| 16 × 14 × 8 in | 304 stainless | 16 x 14 x 8 in | Rated NEMA 4X / IP66 by the manufacturer; not UL listed |
| 20 × 16 × 8 in | 304 stainless | 20 x 16 x 8 in | Rated NEMA 4X / IP66 by the manufacturer; not UL listed |
Questions
Can I buy the factory foam-in-place gasket material for one door?
The chemistry exists — self-skinning two-part polyurethane — but production doses it with metering pumps that hold a fixed mix ratio and a steady bead height. A hand-applied bead varies along the door, and the thin spots leak at the first rinse. For one door, fit a die-cut profile or a 3-6 mm cord compressed 25-35 %.
How much should I compress a polyurethane enclosure door gasket?
Aim at 25-35 % of its free height, the working band gasket datasheets publish for cellular polyurethane and silicone profiles. Below about 20 % the seal leaks across flange waviness; from about 50 % up, the foam takes a compression set and rebounds weakly, so it needs replacing within a season. A cord about 1.5 times the latched gap lands near 33 %.
Does a replacement door gasket affect a UL listing?
A UL listing covers the whole panel as it was listed, so a swapped gasket sits outside it. UL 50E does include a compression test for door gaskets: solid and cellular materials can both be evaluated, though not every material needs it. Our boxes are rated NEMA 4X / IP66 by the manufacturer, not UL listed, so fit the profile the drawing calls for.
How do I test the seal after fitting a new gasket?
Run the paper-pull test described below: even drag around the loop means contact everywhere, and a strip that slides out freely marks under 20 % compression there, usually at the splice. After a 24 h settle, a hose rinse on the door should leave the flange line behind the gasket dry.
