How to Make the Warmest Coat Ever: Interlining with Thinsulate

Earlier this week I shared my Pendleton wool Oslo Coat, by far the warmest coat I own (seriously giving my North Face parka a run for it's money!) While the wool I used was quite thick, and I chose a flannel backed satin for added warmth, the true hero of this project was a Thinsulate interlining and in today's post I'm going to explain how to sew with product, perfect for our Clare Coat or any other coat pattern you may be using.

Editor's note: Since writing this post, we've opened Core Fabrics and now stock a much more eco-friendly interlining made from recycled wool and recycled polyester, so I highly suggest using that instead of Thinsulate, which is made from virgin polyester.

THINSULATE

Thinsulate is a quilted, polyester-filled batting that is engineered specifically for adding warmth to outerwear and sleeping bags. It also works well to fight damp conditions and is made with a blend of polyester and olefin.

The Thinsulate I used for this project is from Club Tissus. They offer it in four weights, ranging from 70 grams to 200 grams. Different weights are appropriate for different temperatures: 70 grams = -10C, 100 grams = -20C, 150 grams = -30C, 200 grams = -40C. Unless you live in the arctic tundra, I would suggest using the 70 or 100 gram weight for coat making. The 150 and 200 gram weights start getting a little thick and may add more bulk than you're willing to live with. Club Tissus sent me Thinsulate samples to test what thickness to go with, and this is what it looks like:

To understand the  thickness between these three options:

TIPS FOR INTERLINING COATS

• Your pattern must be lined in order to interline with Thinsulate or our recycled wool interlining.
• If the garment is close fitting, you may want to consider going up a size, since the batting will add bulk. Make a muslin to determine if this is necessary.
• Order the same yardage that is called for the lining, since you will be interlining the lining pieces, not the body of the coat.
• Make sure you are only interlining the lining pieces. Most coats have facings, and interlining these pieces will create way more bulk than necessary, and interlining the lining lets you avoid bulk around design details like pockets and darts.
• If you have to sew a dart on your lining, cut the interlining away from the dart triangle.
• To choose the right weight, determine how warm you want your coat to be and what kind of climate you live in. The 70 gram would be great for mild winters. Cold winter survivors should look to the 100-150 gram weight. The 200 gram is probably best reserved for sleeping bags and parkas.
• This product melts VERY easily so avoid touching it with your iron. Using a press cloth is very helpful.

Thinsulate Alternatives:  If you don't want to use synthetic material, you can also use wool batting or lambswool in the exact same way I outline below.

SEWING AN INTERLINING FOR WARMTH

When it's time to cut your fabric, cut the interlining using your lining pieces. Now align your interlining and lining pieces, and stitch together just inside the seam allowances; using a walking foot helps keep the layers together without shifting. If you don't have a walking foot, temporary spray adhesive would also help. The seam allowances for this project were 1/2", so I sewed just under (about a 1/16" less than 1/2") to attach them. This ensures when you go to sew all your lining pieces together, you won't see the stitch line. You may also choose to quilt the batting and lining together. It's a bit more work but adds a nice design detail.

One thing to pay attention to is the hems of the lining. You don't want to have the interlining folded at the hem of the lining because it will be too bulky. Once I determined where that hem fold would be, I trimmed the interlining along the bottom so it would just touch the fold of the hem, although I don't have a photograph for this step.

Once all your pieces are stitched together, it's important to grade the seam to reduce bulk (duckbill scissors are our preferred tool for grading seams since they prevent you from trimming the bottom layer accidentally). I suggest leaving around 1/8"; any less than that and the batting may fray.

Once your seams are graded, you can proceed to sew your lining as directed. The seams will be a bit thicker, but pressing with a clapper should help them lay flat.

This technique works for any interlining material, so you can follow the same steps using lambswool, flannel, or primaloft (another synthetic insulator).

Go forth and make those coats as warm as can be!

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