Agglomerated, natural and expanded cork explained

This guide explains the cork material forms. How a cork surface behaves as a pin board is covered in the pillar guide on cork and pin boards. Amorim's process book lists natural cork, granulated cork, agglomerated cork and corkrubber as separate density classes [1], and lists expanded cork board on its own page [1].

For the botany of the tree, see our harvest guide.

The process starts with granules. Amorim says its cork granules are controlled and separated by size and density [1]. For its agglomerated cork cylinders only, Amorim lists a grain dimension of 0.5 to 25 mm [1].

An academic study by Barreca and Fichera describes where much of the granulate comes from. High-quality cork is mainly used to produce bottle stoppers, and more than 75% of it becomes a waste product in that process [3]. The study adds that a large amount of waste cork comes from industry, forest cleaning and pruning, and waste selection, and that this material is recycled and triturated into cork granulate [3].

The granules are then bonded. The study, which concerns insulating boards used in building, says such boards are offered in various versions depending on the binder, gradation and specific density, and cites earlier work in which urethane, melaminic and phenolic resins were tested as binders [3]. It also mentions a method that uses cork's own resin, suberin [3]. Amorim lists its agglomerated blocks as having more than 90% cork content, thicknesses from 0.8 mm to 210 mm and densities from 140 to 600 kg/m3 [1]. It also lists agglomerated rolls with a maximum thickness of 15 mm and a maximum width of 1500 mm [1].

Amorim's list for agglomerated blocks also names different grain sizes, a range of cork patterns and the possibility of adding colour [1]. Its rolls list a minimum thickness of 0.8 mm alongside the 15 mm maximum [1]. For a buyer, this means grain size, pattern, colour and thickness are all things a supplier can state, so put each one you care about in the written specification.

Amorim says the granules go into an autoclave and are exposed to super-heated steam at 350 degrees C. They expand and release their own suberin, and no binders or chemicals are added [2]. The process book gives expanded cork board a density of 100 to 160 kg/m3 and describes its mechanical resistance as low [1].

Amorim sells it as insulation corkboard [2]. Ask the supplier whether a given board is expanded cork.

Amorim gives natural cork a density of 160 to 260 kg/m3 [1]. That figure is for the material class Amorim lists, not for a finished pin board.

The guides do not define a retail 'natural cork board' or a 'bark sheet' pin board, and they set no standard for what a seller may call one. A seller could mean a natural, bonded or expanded cork board, so the label alone tells you little.

Ask for these in writing before you compare boards:

• The cork form: bark, bonded granules or expanded cork.
• The density, stated in kg/m3.
• The grain size and thickness, since Amorim lists both as variables [1].
• The binder: a resin, or the cork's own suberin.

Keep the replies with your sample approval records so the specification you approved is the specification you receive. Then test samples. See pin, cork, magnetic or glass board, the boards buying guide and frame materials. The table below sets out the forms side by side.

ArtzFolio is a private-label manufacturer with a working office and factory in Noida, serving businesses and brands only. Our boards range includes pin boards and cork boards. Tell us the board type you need and we will confirm specifications in the quote, as set out on how quotes are built.

Shipping is EXW Noida and payment is 50% advance. See EXW Noida explained for what that means, or send details through our contact page.

1. Cork Solutions & Manufacturing Processes, Amorim Cork Solutions. amorimcorksolutions.com
2. Expanded insulation corkboard (Amorim Cork Solutions product brochure), Amorim Cork Solutions. amorimcorksolutions.com
3. Thermal Insulation Performance Assessment of Agglomerated Cork Boards (Barreca and Fichera, 2016), Wood and Fiber Science, Society of Wood Science and Technology. wfs.swst.org