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Metal Doors

When it comes to metal doors, Sing Core is one supportive resource behind the scenes that you may not be aware of, and is the proud creator of some of the best metal doors in the industry.

Although metal doors are traditionally incredibly heavy, Sing Core technology gives architects and door manufacturers the ability to create lightweight doors without compromising strength. This is especially true if you are looking for security doors. Additionally, our doors also have the added benefit of being eco-friendly, made in the USA, insulated, and sound-deadening.

It’s very important that doors be operable, especially pocket doors, bypass sliding doors or double sliding doors. If your metal doors are large in size, or in use as steel security doors, then other challenges must be taken into consideration in the architectural design and specification of your metal doors.

Metal Automatic Sliding Door

When looking for the best metal automatic sliding doors, you want hassle-free installation, low maintenance, and high-quality doors. If your sliding door is missing any of these components, it causes undue stress on the automatic sliding door hardware and the structure that houses the hardware. This can lead to more expensive maintenance issues over time. However, Sing Core doors can avoid these issues by providing lightweight, high-strength, and warp-free door cores that are guaranteed to last for up to 50 years.

Large metal automatic sliding doors with Sing Core inside

Warp-free Metal Doors

Only metal doors with Sing Core inside can be guaranteed to remain warp-free for 50 years. This means your metal doors can be guaranteed not to warp, bend, twist or otherwise fail for 50 years, including the full structure warranty of the door. Plus, the lightweight and high strength characteristics of the door, means less maintenance necessary over time, truly a breakthrough in architectural metal door design specs.

Hot Rolled Steel Sliding Doors

These Hot Rolled steel doors are among the lightest weight hot rolled steel doors for the ultimate architectural panel.

Any Type of Metal Doors

At Sing Core we specialize in creating metal doors that weigh a fraction of other metal doors while providing all the added benefits of having Sing Core inside. We can create custom metal doors in a variety of door skins. These could include beautiful materials like brass, bronzecopper, and traditional materials like steel and aluminum. Our two most popular types of metal doors are aluminum sliding doors and steel sliding doors.

Aluminum Doors

Sing aluminum doors are made to the highest degree of accuracy and precision by supporting the best architects, custom metal door artisans, door manufacturers, millworks, and metal work companies. Many types, styles, and weights of aluminum are availability. One favorite material of Sing Core is anodized aluminum. As seen in the image below, the anodized aluminum creates a beautiful work of art that is both functional and unique.  Anodized aluminum can be created in a variety of colors like gold, red, blue, silver, green, or black to create a door that is high strength, lightweight, and visually gorgeous


Metal doors large hot rolled steel sliding door being finished

Large hot rolled steel sliding door being finished

Steel Doors

Our most popular metal doors are created using a variety of different steels. All of our processes create high-tech, ultra-exclusive, and beautiful metal doors. See examples of our cold rolled steel doors, diamond plate steel doors, galvanized steel doors, hot rolled steel doors, or stainless-steel doors in our galleries below. These doors can be custom manufactured to your architectural specifications with Sing Core inside.


An architect demonstrating the ease of closing a Sing Core steel door.
Sing Core steel door recently installed at Nike headquarters.
Unfinished Sing Core steel sliding door. Check below to see it finished.

Cold Rolled Steel Doors

Metal doors cold rolled steel sliding doors

Cold rolled steel sliding doors

Hot Rolled Steel Doors

Metal doors large hot rolled steel sliding door

Large hot rolled steel sliding door

Galvanized Steel Doors

Lightweight one-inch galvanized steel door panel strength demonstration

Lightweight one-inch galvanized steel door panel strength demonstration

Diamond Plate Steel Doors

Metal doors modern diamond plate steel door lightweight stronger than steel

Modern diamond plate steel door lightweight stronger than steel

Stainless Steel Doors

Multiple steel panels can be joined on site to create large stainless steel doors

Multiple steel panels can be joined on site to create large stainless steel doors

Metal Exterior Doors

Metal exterior doors can pose additional challenges, especially if one side of the door is 100% exposed to the elements. Without Sing Core door cores, doors are prone to warping because of the changes of environment. However, by using Sing Core you avoid the issue of warping. The patented Sing Core design can guarantee your door’s structural integrity for up to 50 years

Metal doors with closed edges

Metal doors with closed edges

Metal Kitchen Door

metal doors insulated for cold storage

Insulated cold storage

Whether your application is interior or exterior, Sing Core can help your favorite metal door company to build the best metal doors to your specifications and expectations. We can create metal kitchen doors, cold storage metal doors, or insulated metal doors.

Serving the Top Metal Door Manufacturers in the World

Sing Core provides professional Sing Core metal door core to the top four metal door manufacturers in the world enabling them to create a high precision, high performance custom metal doors. All our products are Eco-friendly, made in the USA, lightweight, and high strength. Our  metal doors are guaranteed not to fail for 50 years. You get the ultimate door and core that the planet has to offer.

See also: Metal Sliding Door Gallery

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Sing Door Ship Receive Warp-free Care

Shipping, Receiving, and Care of

Your Warp-free Sing Door

Sing Core only works with the best and most highly proficient millworks and door manufacturers. This segment of the industry is well-versed in how to deal with high-end building materials such as Sing Core. For many years, Sing Core has provided unfailing warp-free solutions to the biggest and best architects and millworks in the world, without one complaint.

As more millworks and smaller door companies are reaching out to offer their clients access to Sing Core, we do occasionally run across industry professionals who are not aware about what to expect or how to handle Sing Core raw materials. Some of these less-experienced, newer and/or smaller millworks and door companies may not know what to expect when dealing with a product like patented Sing Core. We desire to welcome newcomers to have access to patented Sing products. For those, we are providing the following information:


All Sing products are shipped as unfinished to the millworks and door companies who are highly proficient in working with high-end materials such as Sing Core. A Sing door blank is not a ready-to-install door and are not available from the factory with hardware or as pre-hung doors. Sing Core works in tandem with the industry professionals and the factory may, or may not, handle some of the detail works, such as applying exterior skins to the door blank. The door finishing, hardware, framing, and installation are all coordinated before your Sing door blank is built.

Packaging and Shipping

Sing products tend to be very large in size and require custom crating to assure they are not damaged in shipment to the industry professionals. Even with the best efforts of Sing Core’s custom crating team, sometimes a Sing product may arrive blemished and/or damaged by the shippers entrusted with the handling of crated Sing materials. In most, if not all, cases the level of structural integrity of Sing products in combination with the high level of proficiency of the finishers receiving Sing products, even damaged Sing Core can easily be returned to new condition, even if mishandled or damaged in shipment.

Arrival of Sing Products

Upon arrival of Sing products, be prepared to receive an unfinished product via truck. Offloading may require a forklift and dock for receipt. That said, there will be work that needs to be done to the product received by the millwork or door company before it is retail-ready.


In most cases, when receiving a multiple Sing Core order, where Sing door blanks have been shipped in a stack, or side by side, it is perfectly normal for even a warp-free door blank to appear to be warped upon receipt. Usually, the Sing door blank(s) which face the outside of the crate, or the top of a stack of warp-free door blanks will appear to be warped. By acclimatizing these doors, they will straighten out to their straight and true flat appearance.

To acclimatize your Sing door core, stand your door on its edge at least twelve inches away from any adjoining surface area, allowing it to acclimate for up to 72 hours. Measure your door again and you will find it to be straight and true. If not, document for warp and contact Sing Core.


After you’ve received your patented Sing products, in the event that you will have to store them prior to finishing and/or installation, try to store them standing upright, on end, with plenty of space in between. Do not lean Sing products against a wall. If you have to store them stacked, wrap in plastic and place one or two sheets of plywood underneath and on top of the stack of Sing products. This will help keep the entire stack similarly acclimatized while not in use, otherwise, you may have to re acclimatize the top and/or bottom Sing products later, when you are ready to use them.

Door Warp Definition

Door warp is a variation from a plane surface within the door itself. It does not refer to the door in relation to the frame or jamb in which it was hung. Bow, cup, and twist are terms which describe warp in a door and are defined as follows: Bow is a curvature along the door height, or a deviation from a flat plane from end to end. Cup is a curvature across the door width or a deviation from a flat plane from side to side. Twist is a distortion in which one corner is out of the plane of the other three corners. Warp is usually a result of unequal stresses within the door from one face to the other caused by changes in humidity and temperature conditions or uneven conditions from one face to the other. Buildings shall be humidity and temperature controlled before doors are delivered and installed. Required conditions are 25% to 55% relative humidity and 50° to 90° F (10° to 32° C) temperature range. Improper handling, stacking, and storage can also contribute to warp. Doors shall be stored flat on a level surface off the floor with cross supports.


Use a taut string or straight-edge and measure on the concave face of door – diagonally, horizontally, or vertically. Measure at the point of maximum distance between the taut string or straight-edge and the face of the door.

Measurement must be made on the concave face of the door. Door shall be open when measuring for warp (lock not latched into strike). One person can measure warp using a string and taping one or both ends onto the face of the door, holding it taut. Don’t measure warp in relationship to the door frame. Often a door may not fit into the frame properly but is not warped. In these cases, check the frame – it must be set plumb and square and jambs must not be twisted or out of alignment. Action on any claim for warp may be deferred for up to one year after project completion to permit doors to acclimate to temperature and humidity conditions.



1-3/4 inch (44 mm) or thicker doors:

  • 3’-6” x 7’-0” (1050 mm x 2100 mm) or smaller, 1/4 inch (6.4 mm) maximum.
  • Larger than 3’-6” x 7’-0” (1050 mm x 2100 mm), 1/4 inch (6.4 mm) maximum in any 3’-6” x 7’-0” (1050 mm x 2100 mm) section.

1-3/8 inch (35 mm) doors:

  • 3’-0” x 7’-0” (900 mm x 2100 mm) or smaller, 1/4 inch (6.4 mm) maximum.
  • Larger sizes not addressed in this standard

Warp-free definition: Doors with patented professional SingCore inside outperform any other Eco-friendly door in the world in terms of being lightweight (SingCore weight is approximately 10 % of solid wood, timber or plywood core) and high strength (660 PSI+, stronger than steel pound-for-pound). No other door Eco-friendly door made in the USA can reach our high precision (SingCore approximately +/- .006 inch) or flatness meets or exceeds door industry allowance for door warp, as seen above). We guarantee no other Eco-friendly, lightweight, high-strength insulated door can compare with any door that has patented professional Sing Core inside. SingCore is raising the standard of what is possible in terms of building large doors that can be true flat and warp-free.

How can you tell if you have a warped door or not?

There is an industry standard method of determining whether your door is warped or not.

To determine whether you have a warped door or not you will need a length of string (longer than the length or height of your door) and a measuring stick or tape measure.

a) Tape one end of the string to the edge of the door and the other end to the opposite edge of the door.

The string should be straight. If there is a gap between the string and the door’s surface, you may have a warped door.

b) Measure the gap between the string and the door’s surface area.

If the gap is greater than ¼” your door is warped (according to AWI standards for 1-3/8 to 1-3/4 inch doors 3’-0” to 3′-6″ x 7’-0”).

c) If the length exceeds 7 ft. AWI standard applies to any 7 ft. section. Apply string to any 7 ft. span.

Contact your door maintenance company and send them two photos.

d) [1] Photo of the length of the string which shows as much of the door in its entirety, or at least from one end of the string to the other. Then [2] a closeup photo of your measurement of the gap.

Armed with these two photographs, which can easily be emailed to the millwork or door maintenance company of your choice, the recipients will be able to determine how best to approach the repair or replacement of your warped door.

You might consider replacing your warped door with a professional door which has Sing Core inside which can be guaranteed not to warp, bend twist or otherwise fail so as to avoid this pitfall in the future.

For more information, see: Door Warping vs. True Flat

What if my door with Sing Core inside is warped?

The same standard method of determining and measuring any door with Sing Core inside is used just like any other door (as noted above).

Contact Sing Core about your concerns about your door being certain to include the two photos as noted above.

If you have purchased a professional door with Sing Core inside, you may be the recipient of a replacement Sing door.

Note that upon arrival and un-crating of a door with Sing Core inside, a door may appear warped (and indeed it will be measurable). This is normal for a door which has been packed and in transit. Stand your door on its edge at least twelve inches away from any adjoining surface area, allowing it to acclimatize for up to 72 hours. Measure your door again and you will find it to be straight and true. If not, document for warp (as above) and contact Sing Core.

In the event that a professional door with Sing Core inside is warped (which is highly unlikely) your help in determining the cause of the door’s warping is appreciated. Please assist documenting the chain of custody of your professional door with Sing Core inside, including the millwork or door company which finished the door, and the installers who installed the door, to help us insure your replacement door remains warp-free.

See Also: Sing Core Definition of Terms


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Only Warp-free Large Door Guaranteed

Warp free large sliding doors by Sing Core

“I love these doors.” *

This photo depicts the installation of some of our latest warp-free large sliding doors. These Eco-friendly lightweight, high-strength professional Sing large sliding doors are 12 ft. tall, 68 inches wide and only 1.5 inches thick, and guaranteed not to warp, bend, twist or structurally fail for a full 50 years. When we say lightweight and high-strength, we mean it. For example, these Birch (1/4″ facings) large sliding doors weigh in at 150 lbs. per architectural specifications of Carol A. Wilson FAIA.

* = Linda Rice of Kercor Construction

The Only Warp-free Large Door Guaranteed

Large doors used in high end construction, luxury homes and mansions cost between $10,000 and $50,000 and all of them either are guaranteed to warp or guaranteed not to warp for (at the most) one year… except for one.

Our #1 job is to serve the door companies who make the best doors, so they can deliver warp-free doors to their most discriminating clientele.

$20,000 Door + 1 year = Warped Door

Warping large doors are burning moneyWhen a customer requests and the architect specifies a large door, especially a large sliding door or large pivot door, most door manufacturers will be reluctant to build it. If they do build it, they are not likely to offer a warranty for warping or structure failure because, unfortunately, large doors will warp.

Some offer a one year warranty and charge an extremely high professional for the large door, because they know it is likely that the door will warp. They install the door and pray… after one year has passed (either with or without service calls to straighten the door due to seasonal changes), they wipe the sweat from their forehead, then the burden for maintenance of the large door fall on the customer.

Large doors present a high degree of challenges because large doors (over 7 ft. tall) will warp.

The Only Warp-free Doors

Guaranteed for 50 Years

True Flat Guarantee premium certified true flatEvery door manufacturer who has sought out Sing Core as their large door solution knows there is no other way to make a hassle-free non-warping large door.
In fact, Sing Core door substrates are the only composite door core material that can be guaranteed not only to be warp-free but also maintain full structural integrity for a full 50 years.

High-end Door Manufacturer’s Secret Ingredient

Sing Core works with high end door manufacturers and millworks specializing in the most exotic oversized (therefore problematic) doors.

“When the door manufacturer calls us, they know, we know, everyone knows that custom large doors will warp. We help them solve the problem so they can deliver a product that will not fail to their clients who desire only the best doors without fear of warping.”

If you’re seeking out a high-end door that does not warp, ask your door manufacture to build your door with Sing Core Inside.

Infinite Structure

Patented Sing Core infinite torsion box 2x2 structure grids insulation

Infinite 2×2 in. grids filled with rigid foam

Sing Core’s internal vertical grain torsion box structure is reduced to form 2 inch x 2 inch grids and the torsion box voids (empty spaces) are not left empty; they are filled wall-to-wall with rigid foam insulation to add shear strength and form a high precision (.006 in. tolerance) solid composite substrate. The grids run infinitely in all directions throughout the door core resulting in a warp-free, lightweight (a fraction the weight of other heavier materials), high strength (660 PSI) that is pre-insulated (R3.5-R5.5).

Is There Any Other Way to Make a Warp-free Door?

Yes. There are many ways to make a steel door that does not warp. These large steel doors are extremely heavy (thousands of pounds). To address the issue of weight, lighter weight steel doors are made by using a steel frame (with internal steel pipe substructure) welded to thick steel exterior to make the steel door lighter than a solid steel door.

10 ft x 5 ft x 2.25 inch center pivot door solid maple wood stave warp free

Solid Maple Wood Stave 10 ft. x 5 ft. x 2 1/4 in. Warp Free Center Pivot Doors

Even so, not only is the resulting door still extremely heavy, it is hollow in between the inner steel structure. This space between the inner steel framing is left open, i.e., hollow. There could be 8 to 12 inches between steel bars (or other type steel interior frame) of nothing, only hollow space.

Normally, steel doors – while they may not be a problem for warping – are less high precision due to all the interior welding necessary to manufacture the steel door. To increase the steel door’s precision, the door can be made slightly oversize and machined to straighten the surface area imperfections.

Sing Steel Doors

On the other hand, steel doors made with solid Sing Core door substrate are Eco-friendly, lightweight, high strength and high precision (Sing Core is +/- .006) as well as fully insulated for temperature/climate control and sound deadening qualities. See: Steel Doors

New Large Door Technology

Eco-friendly Sing Core technology is changing the landscape of all large door manufacturing. Sing door core substrate can be used to manufacture any type or style of door in any size (up to 50 ft.) with any exterior material, including wood doors made of any available natural wood species, aluminum doors, ceramic doors, concrete doors, fiberglass doors, glass doors, HPL doors, Kevlar doors, Masonite doors, plastic doors, steel doors (cold rolled steel doors, galvanized steel doors, hot rolled steel doors, etc…), just to name a few…

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