If you’re making or repairing waterproof clothing or equipment, the fabric itself is only part of the equation. The moment you stitch two pieces of waterproof fabric together, the needle creates small holes that can provide a route for moisture to get through.

Even when water doesn’t pass directly through a needle hole, the stitching thread can absorb moisture and transfer it from one side of the fabric to the other.

That’s where seam sealing comes in.

There are two main options for sealing stitched seams: seam sealing tape and liquid seam sealant or adhesive. Both are designed to help stop water passing through the stitching, but they work differently and suit different applications.

What is seam sealing tape?

Seam sealing tape is applied over the inside of a stitched seam. It has a heat-activated adhesive which bonds the tape to the fabric, covering the stitching and creating a sealed seam.

It’s commonly found in waterproof outdoor clothing and equipment, including:

• Waterproof jackets
• Mountain jackets
• Ski jackets
• Tents and camping equipment

Seam sealing tape can be a particularly good option when making a new item from scratch. You can plan the construction of the item with seam sealing in mind, making the seams easier to access when the tape needs to be applied.

Different seam sealing tapes are designed for different types of fabric and coating. For example, there are tapes intended for PU-coated fabrics and others suitable for breathable three-layer waterproof fabrics.

Choosing a compatible tape is important, as there’s no guarantee that every seam sealing tape will bond effectively to every fabric.

How do you apply seam sealing tape?

The tape is normally applied to the inside of the seam with the adhesive side facing down.

A layer of heatproof paper, such as baking parchment or suitable Teflon paper, can then be placed over the tape and fabric before heat is applied with an iron.

This protective layer is important. Many waterproof fabrics have delicate coatings which could be damaged, melted or shrunk if an iron is placed directly against them.

The aim is to allow enough heat through to activate the adhesive without damaging the underlying material.

Always follow the instructions supplied with your seam sealing tape, as the appropriate application will depend on the product and fabric being used.

What is liquid seam sealant?

The alternative is a liquid seam sealant or seam sealing adhesive.

Rather than covering the seam with tape, the liquid is applied to the seam so that it fills the small holes created by stitching. It then dries or cures to leave a seal.

A suitable seam sealant remains flexible once cured. This flexibility is important because a very rigid material could crack as the fabric moves, potentially opening the holes again.

Liquid seam sealants can be easier to apply than tape, particularly when repairing an existing item.

The trade-off is appearance. Because the cured adhesive remains visible on the inside of the seam, it may not produce quite as neat a finish as properly applied seam sealing tape.

Why does seam sealing tape come away over time?

It’s not unusual for the seam tape inside an older waterproof garment to begin detaching.

Repeated washing can contribute to this deterioration. Tumbling and spinning can gradually affect the bond, while washing at an excessively high temperature may also cause problems with the adhesive.

Age is another factor. Older seam tape can eventually degrade to the point where it becomes powdery and begins breaking away rather than simply peeling off in one strip.

Following the garment manufacturer’s washing and care instructions can therefore help preserve both the fabric and its sealed seams.

Seam sealing tape or liquid: which is better for repairs?

Replacing tape on an existing garment can be fiddly.

Think about trying to position and heat a narrow strip of tape accurately around the inside of the armpit of a waterproof jacket, for example. There are awkward angles to negotiate, and you also need to know that the replacement tape is compatible with the original material.

In these situations, liquid seam sealant can offer a practical alternative.

Just because an item was originally manufactured using seam sealing tape doesn’t necessarily mean it has to be repaired with tape. If you’re not confident applying new tape, an appropriate liquid seam sealing adhesive may be easier to work with.

Can you use seam sealing tape on heavy fabrics?

Seam sealing tapes tend to be better suited to lighter fabrics.

As a general guide, the tapes on our website are typically suited to materials below around 400gsm. Heavier fabrics can be relatively stiff compared with lightweight seam tape, potentially making it more difficult to achieve a reliable bond.

For heavier materials, a liquid seam sealant may therefore be worth considering instead.

Choosing the right seam sealing product

The right choice depends on what you’re making or repairing.

For a new waterproof garment or lightweight outdoor project, seam sealing tape can provide a neat and effective solution, particularly when the item has been designed with accessible seams.

For an existing garment, awkward seam or heavier material, a liquid seam sealant may be simpler to apply.

Most importantly, check that the product you choose is suitable for the fabric and coating you’re working with.

Explore Point North Profabrics’ range of seam sealing products and find the right solution for your next waterproof clothing, repair or outdoor equipment project.