High Society Kustom Garage

Seams for Auto Upholstery

Seams like a stitch-up

An introduction to seams

Before you have a car retrimmed, seams for auto upholstery are probably not something you’ve ever thought about.  After all, it’s not exactly a selling point for a vehicle.  Besides, why would you have needed to worry about them?  Well, any decent trimmer prides themselves on crafting neat seams.  A well-executed French seam can be extremely satisfying to create, and a source of pride to a trimmer.  But there are good reasons to care beyond the professional pride of your craftsman.  Each seam must perfectly join separate pieces to conform to the trim’s shape.  The seam should be strong enough to survive its intended use, while also looking attractive. Or at the very least not catch your eye for the wrong reasons.

Here are some of the more common seams used when trimming a car.  Each has its advantages, but sometimes it just comes down to a style choice. So, let’s look at 5 common seam types and where you’re likely to find them.

Basic seam

The main function of all seams is to hold 2 pieces of material together.  The simplest type of seam is the basic back-sewn seam.  To sew a basic seam, your trimmer will place both pieces of material face-to-face, then stitch through both pieces on the backside. They will take care not to stretch either piece when stitching and to keep the sewing allowance aligned.  Depending on the trimmers’ preference, the sewing allowance (the bits hidden inside the trim) will be 10-12mm most times.  They’ll stitch about 1cm in from the end, backstitch, and then stitch forward along the seam line.  Finally, they’ll secure the seam by backstitching at the other end.  All seams adhere to the basic process of aligning fabric pieces and sewing.

The basic seam is usually found between panels on a seats insert and as the joining seam on suspended headlinings.  It is also used where the insert meets the bolster on deeply bolstered seats.

Basic back-sewn seam used on all joins.
Backsewn basic seam.

Top-stitched seams

While there are different variations of top-stitched seams, the most common are either a single top-stitch or a French seam.  Depending on the application, a top-stitched seam can increase the strength of a seam, help with fitting by laying the sewing allowance a certain way, or be purely decorative. 

Single top stitch

The single top stitch starts by sewing the basic seam. The sewing allowance of both pieces is then folded one way, creating three layers on one side of the seam.  A second stitch line is then run parallel to the first through all three layers.  This second stitch is usually between 3 and 5 millimetres from the first.  To create a good top stitch, the correct tension settings must be set on the sewing machine.  Second, it needs to be sewn at a consistent distance from the first.  This is because the entire stitch line is visible and is often sewn in a contrasting colour to the material.

A variation of this seam can have the sewing allowance on the side of the fold trimmed back before sewing to reduce bulk.  Another variation of the single-top stitch is actually a double-top stitch.  Here another parallel line of stitching is sewn on the same side of the basic seam.  This is not to be confused with the French seam.

This seam is primarily used on seat borders, door trims, dashboards, and consoles.  Anywhere that a decorative stitch is wanted.  Especially where having the bulk on the sewing allowance laying in a particular way would be beneficial.

Single top stitch seam in contrast thread on left. Double top stitch on border seam on right.
Single top stitch seam in contrast thread on left. Double top stitch on border seam on right.

French seam

Once again, your trimmer will begin by sewing a basic seam.  Like a top-stitched seam, the sewing allowance will be folded and stitched through.  Where a French seam differs though is how the allowance is folded.  In a French seam, the sewing allowance is opened up to either side of the seam.  One stitch line is then run on either side of the seam, each through two layers of material.  Again, machine settings are important, the thread tensions will need to be set correctly.  This time, two visible stitch lines will need to be run perfectly parallel to the seam.  Any deflection will stand out like the proverbial, especially with a contrasting thread.

Variations of this seam can vary depending on its location and purpose.  On a seat bolster, the trimmer may reinforce the seam by adding a backing strip before top-stitching.  This would never occur on a seam where there is an airbag though.  Another variation would be more of a fake French seam, on a dashboard for instance.  Here, the sewing allowance is cut away before top-stitching to remove all bulk.

Other places a French seam may be found are on the console lid and on armrests and door handles.  New cars and modern style builds commonly favour French seams.

French seam close up.
French seam close up.

Piped seam

A piped seam differs from top-stitched seams in that the decorative element isn’t added after the basic seam is sewn.  Instead, the piping is usually sewn into one panel first, then the adjoining piece is added.  Some trimmers will save time by sewing both elements in one run, but this is the exception to the rule.

The normal process for sewing a piped seam takes a few steps.  A length of material is cut to a suitable width.  It will need to wrap the piping cord and have the desired sewing allowance on either side.  This piece is then folded in half along its width with the piping cord in the fold.  It is then sewn along the length of one piece to be seamed.  This stitch line shouldn’t be too close to the piping cord, so it is hidden later.  Next, sew the corresponding piece to the half-finished seam.   As a result of having two stitch lines close together, care must be taken when the second run is sewn.  This stitch needs to wrap the cord tightly and keep the first hidden in the sewing allowance.  Correctly fitting a piece with piping has the entire length of the sewing allowance lying on the same side.

Altering the thickness of piping cords changes the appearance of a piped seam.  A smaller diameter can look slightly more modern.  The material chosen for the piping can differ from the panels themselves for a bit of contrast.  Another variation can be made by adding a top stitch next to the piping.

The piped seam is primarily used on seat borders, door trims, and consoles.  Like a top stitch, anywhere a bit of decoration is desired, but where the piping’s bulk isn’t an issue.

Piped seam close up.
Piped seam close up.

Hand sewn seams

Hand-sewn seams describe the group of seams where a large part of the seam is done by hand.  This can still include machine stitched elements on some of the seams.  Sometimes the seam is actually joined by hand, and other times, the hand-stitch is only cosmetic.  The best example of a hand-stitched seam would be on a steering wheel.  Other common uses are gear knobs and handbrake handles, and door and grab handles on vehicles where they’re wrapped.

At first glance, most of these seams probably look the same, but there are actually quite a few common examples.  The skip-stitch diamond also called the Euro stitch, and the baseball stitch are two used frequently. The cross stitch is another.  A less used hand-sewn seam is the parallel stitch, which looks a little like a French seam.  Another example is the square stitch.

While a well done hand sewn seam looks great, just remember that it takes longer than machine sewing.  Of course, this will be reflected in the price.  This is why these seams are usually used for items that can’t be sewn with a machine.  A baseball stitch around the perimeter of the front and rear seats will possibly add multiple days to the job.

Skip stitch hand sewn seam.
Skip stitch hand sewn seam.

Putting it all together

Hopefully you’ve now got an understanding of different seam types, their uses, and how much labour goes into each.  With any luck, this can help you and your trimmer find the perfect design for your new interior.  Bear in mind that most interiors will require a combination of seam types.  However, being consistent with seam type, stitch length, and top stitch spacing will help things look cohesive.

An example of combined seams on one seat.
An example of combined seams on one seat.

Looking for your perfect auto upholstery seams?  Located halfway between Brisbane CBD and the Sunshine Coast, we are perfectly positioned to be your partner in comfort and style.  Call HSKG to make an appointment today.

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