ᐅ Kallax Shelves Are Bowing – Which Is Better: Plastic or Wood?

Hello everyone,

I bought an Ikea Kallax shelving unit and am in the process of setting it up. However, I have a problem with the longer shelves bending over time, especially when I place heavier books or binders on them. Now my question is: For Kallax shelves, are wood or plastic options better to prevent bending?

I am interested in how the different materials compare in terms of load capacity, long-term stability, and appearance. Has anyone had experience with whether it’s better to use the wood shelves or the plastic ones?

I look forward to your opinions and advice!

Hello kagiken,

regarding your question about Kallax shelves: Generally, the standard Kallax shelves are made of particleboard with a melamine coating, similar for both the wood and plastic versions. The shelves are designed for an even load of about 13-15 kg (29-33 lbs); beyond that, they tend to bend.

On your main points:

1. Load capacity: Wood (particleboard) and plastic shelves from Ikea are often quite similar in dimensions and construction. The material thickness is usually the same, so bending mainly depends on the span length.

2. Stability: Wood shelves may slightly warp due to moisture, while plastic shelves are usually more dimensionally stable under moisture but do not necessarily offer higher load capacity.

3. Aesthetics: This is a matter of personal preference.

My advice: If heavy loads are planned, it’s recommended to add support braces or brackets, or to distribute the weight across several compartments. Alternatively, you might consider using a thicker or specialized wooden board as the shelf.

Best regards

REOHEINRIC schrieb:
Wooden floors can warp slightly due to moisture, while plastic floors are generally more dimensionally stable with moisture

I slightly disagree – the standard plastic floors at Kallax are often thinner and more flexible than the wood particle boards. Plastic alone does not automatically mean more stability, especially when it involves thin MDF or particleboard with a plastic surface layer.

In my experience, a plastic floor tends to bend more under load because its material stiffness is lower than that of well-pressed wood.

And let's be honest: wood appearance simply looks better than plastic. If stability is important, you shouldn’t cut corners on materials but rather complement with special plug-in shelves or metal braces.

My point: People who think plastic provides greater load-bearing capacity underestimate the physical properties of the materials. It’s more important to focus on the construction than just the surface. 🙂

Hello kagiken,

I would like to add some more detailed information on the topic "Kallax shelves bending – which is better, plastic or wood?"

First, a brief overview of the materials:

- Most Kallax shelves are made of particleboard. The difference usually lies in the surface finish (wood-patterned foil or plastic).
- Plastic shelves in the Kallax range are generally thinner and coated with a plastic layer, which does not significantly improve stiffness.

Some important points regarding load capacity:

1. Load-bearing capacity mainly depends on the thickness of the panel, the span, and the stiffness of the material.
The standard Kallax width is about 77cm (30 inches), which can be problematic for thin particleboard shelves when storing heavy items.

2. Wood shelves may swell when exposed to moisture if the surface coating is damaged – this causes the board to flex more over time and increases sagging.

3. Plastic shelves tend to deform more under constant load, especially when they are thin.

4. A crucial factor is reinforcement: there are special support braces available for Kallax that can be mounted underneath the shelves. These are far more effective than just choosing between plastic or wood.

Summary and recommendation:

- When it comes to material choice alone, solid wood shelves, especially plywood or MDF with greater thickness, are the best option, as they are considerably more rigid.
- In the standard Ikea range, it hardly makes a difference since both variants are based on particleboard.
- For high load demands, I recommend adding reinforcements afterwards.

Hope this helps!

Interesting discussion so far. I would like to add some technical details to take a deeper look at the question "Kallax shelves bending – is plastic or wood better?"

Shelves are primarily evaluated based on two mechanical properties: modulus of elasticity (stiffness) and flexural strength.

1. Modulus of elasticity:
- Particle boards (wood-based) typically range between 2000 and 3500 MPa.
- Common plastics like ABS or PVC generally have values around 2000 MPa or lower.

2. Flexural strength:
- Wood-based materials vary depending on quality but are usually better suited to carry loads over larger spans.

3. Influence of panel thickness:
- Stiffness increases with the cube (third power) of thickness, so investing in thicker shelves pays off much more than focusing only on the material.

For Kallax, 16 mm (0.63 inch) thick particle boards are commonly used for both wood and plastic coatings. This means the weight you place on the shelves should be evenly distributed and kept within reasonable limits.

A tip:

For heavy loads, consider a two-part construction: for example, cut a thicker multiplex plywood to size and combine it with a thinner shelf board. Alternatively, reinforce the shelf with metal supports.

Finally, a question for you, kagiken: What exactly do you plan to load the shelves with? Books, devices, or decorative items? The type of load affects how weight is distributed.

I look forward to your answer to provide more tailored advice.