Explanation of cladded, disc-bottom and casted cookware constructions
There is a relatively large number of different cookware materials and construction types available. Here we compare the different materials and types of cookware and go into depth about the underlying principles of heat transfer. Pots and pans are produced in different ways. The most common are ply/cladded, disc-bottom and casted cookware.
Clad constructions allow us to harness the positive attributes of different materials. For example, cladded pots and pans often contain an aluminum layer wrapped in stainless steel. This allows us to profit from aluminum’s great ability to transfer heat. At the same time we do not have to worry about its high food reactivity. Furthermore, stainless steel’s properties make the cookware more durable, corrosion resistant, induction compatible and dishwasher safe.
Compared to very common disc-bottom constructions, the body of cladded cookware consists of one piece. This eliminates weak points, contributes to a longer lasting product and increases the ability to distribute heat up the rims.
The most common types of cladded cookware are so called 3-, 5- and 7- Ply constructions. Contrary to popular belief (and due to misleading marketing), the amount of clads does not indicate the quality or performance of a frying pan or cooking pot. Instead, the material, the thickness of each material layer and the overall thickness of the frying pan makes the difference. So don’t let yourself be fooled by any marketers who advertise a 5-Ply copper core construction. Always take a closer look.
In a cladded construction, the different materials are bonded together. Each bond represents a minor obstacle for the heat to pass through. Therefore, in a well engineered fry pan, every material layer serves a specific and desired purpose to increase the overall performance of the pan. It should outweigh the negative aspect of not using one homogeneous construction.
Stainless Steel – Aluminum Constructions
As noted, sometimes the advantage of cladded material lies less in the heat performance but in reducing cookware’s food reactivity and/or improving its stability or design. This becomes obvious by looking at an exemplary 3-Ply construction consisting of stainless steel – aluminum – stainless steel.
In fact, a pure aluminum pan of the same weight shows better heat transfer and distribution than a cladded pan. However, a pure aluminum pan needs to be coated (typically on the inside and outside) to protect against food reactions and would be less durable.
In a 3-ply construction, on the other hand, we benefit from the steel’s stability, superior look, heat capacity and durability as well as the aluminum’s good thermal conductivity, low weight and low cost.
In comparison to a typical 3-ply construction, a 5- or 7-ply construction contains one or two additional layers of aluminum and steel, respectively. As a result, a 5- or 7-ply construction with the thickness of a 3-ply construction does usually contain more steel compared to aluminum, resulting in poorer heat transfer and distribution but better ability to store heat.
7-ply steel-aluminum constructions are supposed to increase durability and heat conductivity. Whereas more steel might protect cookware from warping (which otherwise requires a complex modelling-based calculation), all our internal tests favor the use of copper.
We have shown here that copper transfers heat 20% better that aluminum and 2,800% times better than stainless steel. Copper also has a higher heat capacity and offers more heat control. An aluminum pan with the same heat capacity of a copper pan (increases thickness of the aluminum pan) is only half as good in terms of heating-up the frying pan. This is why copper is regarded as a superior cookware material.
Copper’s performance may be unrivalled in many regards. However, it comes at a steep price. First, the raw material is far more expensive than aluminum. Second, the bonding process is significantly more difficult.
Thirdly, copper represents a special challenge in the manufacturing process. Similar to aluminum, copper shows high food reactivity. Therefore it is often used in cladded constructions. However, especially as part of a cladded construction, copper is difficult to deep draw. The manufacturer requires significant engineering expertise, better tools (the forms used for pressing) and sometimes even a two-step deep drawing process. The reason for this is that adding a third material to the overall construction makes it more difficult to balance pressure and speed of the deep drawing mandrel. If not managed well, copper tends to develop fine fissures and even material cracks. Therefore it is vital that you buy a copper core construction from a brand with the necessary expertise and the willingness to invest in the right equipment.
Copper bonds more easily to aluminum than to steel. Copper is less likely to develop fissures or brittle edges when bonded to aluminum. This is why copper is usually used in a five-ply sandwich construction consisting of stainless steel – aluminum – copper – aluminum – stainless steel.
Less common clad constructions
Besides the cladded cookware construction mentioned above, other types of cladded cookware exist, for example hard anodized aluminum and stainless steel. In 5-ply copper constructions, copper is not exposed. However, other clad constructions exist where the copper is exposed. Most of the time, this is very heavy cookware partly because an increased thickness is required to ensure stability.
Disc-Bottom Fry Pans
The vast majority of cookware in the market are disc-bottom constructions. This type of construction refers to the practice of attaching a disc-like material bottom to a metal bowl. The bowl usually is usually made of either thin steel or aluminum. The disc bottom can have several different constructions (see below).
The advantage of this type of construction is that it allows for the pan to maintain a practical weight while showing good heat distribution across the bottom of the pan. Furthermore, disc-bottom cookware can be cheaper to produce.
The disadvantage is that the cookware becomes less durable and does not conduct the heat as evenly up to the rims of the pan. In our eyes, the design is also less sophisticated. Furthermore, disc bottoms are always a weak-point in the pan and different substances can accumulate in the gaps between the materials.
Two main disc bottom constructions exist, namely cladded bottoms or bottoms made out of one material.
Pure aluminum attachments are the most common one-material cookware bottoms. Those can either be coated or non-coated.
Thin and exposed aluminum bottoms are common and cheap. It is likely that you have such a pan somewhere in the back of your cupboard. They tend to oxidize. Just turn them around at you’ll notice.
Many manufacturers coat their aluminum bottoms in order to avoid corrosion. We’ve tested some very expensive coated aluminum bottom pans and found that coating significantly reduces induction compatability (naturally, aluminum bottoms are not induction compatible. This is why manufacturers started to insert a thin disc-like steel layer)
Most coatings are only safe up to somewhere around 550 Fahrenheit (ca. 300 Celsius) before developing unsafe gases. We are not sure if all manufacturers account for the heat of the flame that hits the coated disc-bottom. Comments are welcomed if you have any information regarding this issue.
Besides pure aluminum bottoms, there exist bottom construction from other materials e.g. pure stainless-steel. Stainless steel bottoms show especially high heat capacity, but very low heat transfer and distribution. In other words, they heat up very slowly but keep the heat for a long time. They show overall low oxidation risk but come at a high weight.
Cladded bottom are the second type of disc-bottoms. These can have the same layer as cladded cookware. Copper is used in disc-bottoms more often than in full-clad cookware. This is because such a construction requires less material and no deep-drawing. At the same time, it still achieves excellent heat distribution at the bottom of the pan. Often, manufacturers make the thickness of the copper layer seem a lot higher. A well-known example is the Anolon Nouvelle Copper.
The type of bowls used on top of disc bottoms
There exist three main types of bowls that are commonly attached to a disc bottom: coated aluminum, anodized aluminum and stainless steel.
Aluminum bodies have the advantage of significantly better heat conduction. Those frying pans show better diffusivity, including up to the rims. However, exposed aluminum pans requires full-body coating to protect against food reactivitiy and corrosion.
Anodized aluminum is marketed to be significantly harder than steel. However, we find this comparison misleading. We might consider a blog article about this issue. Our dishwasher tests revealed that anodized coatings seem to wear off in the dishwasher, too. The photo below shows a frying pan after a few rounds in the dishwasher. After half a year in use, the anodized layer was worn down to the bare aluminum.
Steel bodies have a clear design and oxidization advantage against non-treated aluminum. However, they have very low heat conductivity. So you can say goodbye to optimal heat conduction up to the rims, optimal disc-bottom steel pans have a very conductive disc bottom and a thin steel bowl. This allows for a safe weight and an attractive design and shows great conductivity at the bottom.
Aluminum pans can be manufactured via different casting methods. The naked aluminum body is usually coated on the inside and outside to protect against food reactions and corrosion. Due to the coating, manufacturers struggle with induction compatibility.
Whereas the molds for aluminum are relatively expensive, aluminum cookware is the cheapest type of cookware to produce, no matter what its alloy is (don’t let them tell you any differently). This is because aluminum is cheap and the production process is relatively simple.
There are different types of cookware out there. The most prominent ones are full-clad, disc-bottom and single material constructions. Every type has its advantages and disadvantages.
Fully cladded cookware is more expensive to produce, especially when done with copper. They can have very good heat transfer, including up to the rims, while also lasting a lifetime. Therefore its the most valuable cookware with a great design.
Disc-bottom cookware is less durable but can show even better heat distribution at the bottom. Common aluminum disc-bottom cookware requires a coating in order to prevent oxidization.
Casted aluminum pans are the most common single material solutions. Those struggle with induction compatibility, need to be coated all-round but tend to be lighter while having good thermal diffusivity.