How to spot and block fuse woollen fabric for coat making

Sewing your very own coat, I think, is possibly one of the most satisfying things you can ever make - closely followed by jeans! Sure it takes a bit longer than other types of dressmaking projects but you can get so much more use out of a coat that any other garment. It will go with lots of things in your wardrobe, you can wear it every day and crack it out again each winter for years to come! It’s sewing gold! 

After teaching a lot of coat and jacket making workshops over the past few years, one common question that comes up regularly is whether to block fuse with interfacing the whole of the outer fabric of the coat or just interface certain sections of it. It can sometimes be a tricky one to answer as there are various factors to consider but in this post I hope to give you a better understanding of what it all means and help you work out if you should do it for your outerwear project. 

Just to be really upfront from the beginning, I am basing my tips and suggestions on my own personal experiences after making 7 coats for myself over the last 5 years with various different fabrics and teaching around 7 coat making workshops over the last 2 years. 

In my latest YouTube video I’m chatting all about this and showing you how to do it, or read on for more tips and pictures.

I also have a video and blog post that is more of an introduction to interfacing that you may find useful to watch first if you are still new to using it - tap here to view it.

What does it all mean? Block fusing? Spot fusing? Steam basting? 

Firstly there are a few terms that relate to fusing the interfacing onto the fabric and sometimes you will find terms used interchangeably in different contexts.

Block fusing - In the garment manufacturing industry it means attaching interfacing to the fabric before you cut specific pattern pieces out. So for example, in a garment that has facing pieces, cuffs or waistbands a section of the main fabric would have interfacing bonded to it before those pieces were cut out. 

• Why do it? This makes the process much quicker as you don’t have to cut out the fabric and interfacing separately and then make sure they line up when you bond them together with the iron. Some fabrics might shrink a little or distort off grain before you have attached the interfacing - slippery viscose is a classic example, so block fusing them makes the process more accurate too! 

Block fusing can also apply to the whole of the main outer fabric of a garment when making outerwear. So it means before you cut anything at all out from your main fabric, you attach interfacing to the whole thing. 

• Why do it? If you were making a coat from a woollen fabric, a lighter weight fabric or a fabric that had a looser weave, then block fusing the whole outer fabric can add structure and stability to the garment. It can prevent a saggy, stretched out area over the bottom or at the elbows of the coat as you wear and use it. Overall it can give more longevity to the coat you make. 

Spot fusing 

• This term can refer to adding a small section or patch of interfacing to a certain part of a garment, for example at the top edges of a patch pocket where there is likely to be more stress or pressure on the stitching and fabric at that point as the garment is worn and used. 
• It can also be a step in the process to block fusing a large area of fabric too. So if you had decided you were making a coat and wanted to attach interfacing to the whole of your outer fabric you can spot fuse the interfacing on in small areas (or areas that are about the size of your iron), then cut out your fabric (with the interfacing attached just in those smaller areas). Once the fabric is cut out, then you go back over each piece and properly fuse the interfacing over the whole area of each section of fabric. 

Steam basting - This term pretty much means the same thing as spot fusing means in the second context that I mentioned above - it’s a stage in the process to block fusing a larger section of fabric. 

• Why do it? There is no need to go over a whole large area, properly fusing on the interfacing on as sections of the main fabric will end up being wastage anyway. It’s quicker to just spot fuse/steam baste in smaller areas, then cut out your pattern pieces, then go back over each pattern piece and properly/permanently fuse it on. 

The benefits of block fusing the whole outer fabric for a woollen coat project

• As wool is a natural fibre it will naturally change shape over time, stretch out and mould to your body. If you block fuse it with woven interfacing then the shape and stability of the fabric will be maintained for a longer period, giving your garment more longevity. 

• It’s quicker and easier than cutting out lots of separate sections of interfacing and ironing them on once you have cut out the main pieces. 

• If your fabric is overall on the lighter side in terms of weight, fusing the whole of the fabric can give it more body and help to hold style/design lines of a garment. For example, if the coat has a more a-line shape then this design feature will be better supported and maintained if the fabric is fully interfaced. 

• If the fabric has a loose weave or quite a bit of give in it, for example some boiled wools, then block fusing will prevent the fabric from stretching out as you sew it and then wear the garment. 

What types of weight of wool would block fuse? 

I personally think, if you are making a coat, block fusing most wools is the best thing to do. I have only not done it twice. The first time was the first coat I ever made and I now totally regret it as the coat has gone all limp and floppy and just doesn’t look as slick and sharp as it did when I very first made it. The second time was when I used a wool/cashmere fabric that was very thick, it was basically like a double faced fabric with two layers bonded together. It was the Grainline Cascade Duffle coat that I made and I did still put interfacing on the areas of the garment that the pattern suggested, such as the collar, facings and across the upper back. The fabric just really didn’t need that extra support all over from the interfacing as it was stable and sturdy enough already due to the double layer nature of it. 

If you were making an unlined coat or more of a coatigan style of garment then obviously you wouldn’t want to block fuse that, as you would see the interfacing and also those types of garments tend to be more of a flowing, loose, comfy style anyway. So it needs to be a fully lined garment if you plan to block fuse. 

What type of interfacing to use?

My recommendation would be to use woven iron on interfacing, that’s what I’ve used for the coats that I have made. As the interfacing is woven like regular fabric and has a grainline, it will still allow movement while providing support and the fibres in the interfacing can still move around with the main fabric once its been fused. 

How do you actually spot fuse and then block fuse? 

There are a few ways to do this

• On the ironing board - lay the fabric over the ironing board with the wrong side of the fabric facing up. Place the interfacing, with the rough side (gluey side) facing down so that it is facing the back of the fabric. Make sure the edge of the interfacing is lined up along the selvedge of the main fabric and smooth both layers of fabric out so there are no wrinkles. With the iron on a wool setting and making sure there is water in the iron so that steam can be generated, gently press on the interfacing in several spots over the area of the ironing board. So for a regular sized ironing board 3 or 4 ‘spots’ with the iron should be sufficient. You don’t need to apply a lot of pressure here, I usually just sort of hover the iron over, as steam is generated. This will be enough to hold the interfacing onto the fabric in that one area. Then slide the fabric up to the next section, make sure the interfacing is smoothed out and still lining up with the selvedge and do your next set of spots. 
• As the interfacing is very likely to be narrower than your main fabric, you’ll need to make a join to interface the other section of the main fabric. Repeat the process as above making sure that the two length of interfacing butt up or have a very slight overlap. 

• On a table with an ironing blanket - Alternatively, with you fabric laid out over a larger surface such as a table or even the floor, you could use an ironing blanket (we sell this one by Prym) to protect the underneath surface and do the same process as described as if you were doing it on the ironing board. You’ll just need to keep moving the ironing blanket around underneath to protect the surface you are working on. 

For both methods, once the length of main fabric has been spot fused/steam basted, you then cut out your pattern pieces treating the two layers (main fabric and interfacing) as one. Once they are all cut out, you then need to go back over each piece in turn and properly fuse them together by pressing and steaming them again. Then the pieces are ready to be constructed into the coat.