Down-proof textiles vs. Down migration
What determines the quality of down textiles and what processing tips or seam recommendations play a decisive role to prevent down migration?
From the "Michelin man style" to an elegant, loose fit feather-light look: Down textiles are warm, light and comfortable to wear. Although current fashion trends determine the appearance of high-quality down textiles such as down jackets, vests or coats, functionality coupled with the best possible thermal insulation is usually just as important. The same applies to bedding filled with down and feathers. These should be cuddly and warm. The filling is primarily responsible for the low weight in relation to a high thermal insulation. This can be of very different quality.
What does the filling say about the quality of down textiles?
It is often assumed that the mix of down and feathers alone is decisive for the quality. A relatively high proportion of down, i.e. a ratio of 90% down to 10% feathers, is considered to be high quality while a ratio of 60/40 is seen as average quality. From a technical point of view, a filling of 100% down is not, however, practical since a certain proportion of feathers is required to support the down. Otherwise, the down cannot reach its full volume.
However, the mix ratio is not the only factor that determines the quality of down textiles. The quality of the down and feathers themselves is also important for the volume of the filling. The larger the volume of the filling, the warmer the thermal insulating effect feels. Conversely, this means that a mix with a 60/40 ratio of high-quality down and feathers warms better than a mix with a 90/10 ratio.
What determines the volume of the filling?
If you take a closer look at the bulky filling, it is easy to explain where the volume comes from. Down form the particularly fine under-plumage of the chest and stomach part of geese and ducks and remind of a snowflake in its appearance as they consist of many small, soft and radiating branches with barbs. Unlike feathers, down does not have a shaft or a vane. Instead, it has a very small down core. This gives down its characteristic three-dimensional shape. The larger the individual down, the larger the volume. This voluminous structure allows air to accumulate in the filling, which leads to a particularly good heat-insulating effect.
Feathers, on the other hand, form the visible plumage of waterfowl and have a two-dimensional shape. Feathers therefore have less volume and cannot be pressed together as much as down. This is why feathers have less of an insulating effect than down. The most obvious difference compared to down, however, is the clearly visible and noticeably hard quill. Depending on the quality, the quill can be thicker or thinner and be more or less straight. In general, higher-quality feathers have finer and more sharply hooked quills.
A common problem: Down migration
The quality of the filling is also very important for the overall quality of the product. However, it does not matter whether the down and feathers are premium quality if the filling does not stay inside the garment and penetrates through the fabric or escapes through the stitch holes. This is commonly called 'down migration' or ‘down through’. From a technical point of view, however, this term is not correct and will therefore be discussed further below. Generally, it has to be differentiated whether the filling is penetrating the fabric or the seam.
If the filling is penetrating the fabric itself, it is described as 'not down-proof'. Strictly speaking, this term is not appropriate as it is usually not the down but the quill that penetrates the textile surface.The three-dimensional down, on the other hand, cannot penetrate so easily and if it does, it can only penetrate to a small extent and not completely. The reason for this is the ratio between the size of the down or feathers and the pore size of the fabric. Therefore, the fineness of the fabric must always be matched to that of the down or feather filling. The following applies: The larger the pores in the fabric and the thinner and sharper the quill, the higher the risk that filling material can pass through the fabric. The type of weave of the fabric and the cross-section of the yarn used play an important role here. More densely woven fabrics made of yarns with a flat diameter and as little twist as possible are the most appropriate, e.g. plain-woven fabrics. Alternatively, so-called down barrier layers can also be incorporated in order to prevent the filling from penetrating. They are usually made of fabrics with an extremely dense weave and low air permeability. In addition to the benefit that the barrier layers can prevent down migration, they have the positive effect that darker down and feathers can no longer shine through, especially with light-coloured outer fabrics.
However, the filling can also often penetrate in the area of the seam, or more specifically through the stitch hole made by the needle. The seam or puncture hole is therefore considered the most critical point. If you pull out a single feather or down, others will usually follow. This problem is very common, especially for seams with additional stitching. The relative sizes involved also play an important role in this regard. The larger the stitch hole, the higher the risk of down or feather migration. However, the use of a very fine needle is not always possible. By following certain tips, the problem can be reduced or even prevented.
Technical sewing recommendations
Depending on the design of the down textiles, the fabric pockets that are filled with a down-feather mix can have different positions and shapes. Since these determine the quality of the thermal insulation, it is important to prevent the feathers and down from penetrating to the outside. We recommend to observe the following processing tips:
In general, it is advisable to check the sewability of every fabric prior to processing to see if it is suitable and whether the needle you intend to use is appropriate. To prevent down migration, it is particularly recommended to use needles with a small diameter in order to keep the size of the stitch holes as small as possible.
Using a larger stitch length reduces the number of stitch holes. This also means that the filling material will have fewer potential points of penetration.
The construction of the sewing thread itself can also help to reduce the risk of down migration. The use of rather smooth and even sewing threads prevents down and feathers from sticking to the thread and thus from migrating easily to the outside. In addition, a finer sewing needle can be used to keep the puncture holes as small as possible.
Another factor is the thickness of the sewing thread. The better the stitch hole is covered by the interlacing of the thread, the less likely it is that the filling material will penetrate through it.
The tension settings of the needle and looper threads should be as low as possible. This avoids unnecessarily high tensions between the stitches, which can additionally stretch or even enlarge the stitch holes.
Our thread recommendations
In addition to the processing recommendations mentioned above, the selection of the ideal sewing thread also plays a decisive role in obtaining perfect, down-proof seams. Depending on the material and application, A&E Gütermann offers you various product solutions:
Mara - from light to heavy fabrics
For a uniform and beautiful seam pattern with a ‘cotton look’: Mara is a very fine and uniform sewing thread made of 100% polyester. Manufactured with our unique Micro Core Technology®, Mara is highly tear-resistant and has a very smooth, even cross-section. This allows the use of very fine needles. The small thread loops on the thread surface, the so-called micro loops, can literally hold the down or feathers in such a way that down migration can be prevented.
Tera - for fine to heavy fabrics
Tera, a 100 % polyester continuous filament, is a particularly smooth and even sewing thread due to its construction. Thanks to its particularly fine cross section, the thread loop has sufficient space between the fabric layers, even when using extremely thin, light fabrics. This ensures that the puncture holes are well covered and closed. The filling material therefore stays where it should – inside.
» Our sewing threads are also available with a water-repellent finishing, if requested.
If you still have any questions, our sewing service will be pleased to advise you comprehensively regarding the optimal product solution for you. Please feel free to contact us at firstname.lastname@example.org