Hide Flask in Jackets (Internal Zipper Pockets)
A well-fitted internal zipper pocket can carry a flask without pulling at your jacket or lining. Measure the filled flask, allow room for it to slide in and out, and anchor the pocket to a stable part of the garment. Mock up the fit before sewing, then test the pocket carefully. This is a workmanship check, not a certified load rating.
A jacket pocket should feel like part of the garment, not a lump that shifts when you sit or reach. The main challenges are getting the opening wide enough, supporting the flask’s weight, and keeping the jacket comfortable. A neat design also needs to be easy to inspect and maintain.
I approach this as a small alteration, not a quick cut-and-sew job. First I check the jacket’s lining and seams, then test a mock-up before making any permanent changes. A removable or washable pocket lining can simplify cleaning, but the jacket’s care label still governs how you should wash or dry-clean it. Carry only where permitted, and never use a hidden pocket to evade screening or access controls.
Plan the Flask Fit and Pocket Location
Planning means measuring the flask in the form you will carry it, then choosing a pocket position that supports its weight without interfering with the jacket. Measure the filled flask, including its cap and widest point. Also inspect the lining, seam allowances, and nearby closures before deciding where the pocket can go.
Record three things: the flask’s height, its widest width, and its filled mass. Include the cap in the height measurement and any bulge or corner in the width. A rigid flask may need a little more room than a soft-sided one, especially if the shape is not rectangular.
Allow 10–15 mm of extra internal width and depth beyond the flask’s measured dimensions. Treat this as total ease, not extra space on every side. Too little can strain the zipper or seams; too much can let the flask swing and change the jacket’s drape.
| What to measure | How to check | What to allow |
|---|---|---|
| Flask height | Measure from the base to the top of the cap | Add 10–15 mm to pocket depth |
| Widest point | Measure across the broadest area, cap included | Add 10–15 mm to pocket width |
| Filled mass | Weigh the flask filled as intended | Use this mass for gradual testing |
| Zipper opening | Measure the clear opening, not the tape length | At least 20 mm wider than the flask |
The best location is usually a stable area of lining near a seam allowance, but the jacket’s design matters. Avoid armholes, vents, closures, and structural seams. Do not cut a load-bearing seam to make space. If the available area is too small, choose another jacket or a smaller flask rather than forcing the fit.
Check Access, Movement, and Garment Clearances
A good pocket is easy to reach and close, yet it stays clear of the jacket’s working parts. Before sewing, check the pocket position while the jacket is worn and move through ordinary actions such as sitting, reaching, and fastening the front. The pocket should not block movement or pull the garment out of shape.
Measure the zipper’s usable opening, meaning the clear space a flask can pass through after the zipper is installed. It must be at least the flask’s widest measurement plus 20 mm. The zipper tape may be longer than its opening, so measure between the stops rather than relying on the package size.
Check that the slider and stops suit the fabric. A bulky slider can rub against the body or catch on nearby layers. The zipper tape must be fully captured in the seam, and both ends need secure stitching. Follow the zipper and garment maker’s instructions where available.
Before cutting, pin or baste a pocket from scrap fabric. Try inserting and removing the flask several times. Zip and unzip the pocket, then sit, bend, raise your arms, and reach forward. Look for pulling at the front closure, a blocked vent, or pressure against the body.
If the flask’s contents could leak, consider whether the material and construction can be cleaned safely. Do not assume a pocket is leakproof. A separate sealed container may reduce mess, but it does not replace checking the flask’s cap and following the jacket’s care instructions.
Build and Reinforce the Internal Zipper Pocket
Construction is the process of attaching a pocket bag and zipper to stable garment material, with enough reinforcement to spread the load. Use fabric with a documented specification when possible. If you cannot confirm its suitability, make and test a sample first; a light jacket lining alone may tear even when the zipper remains intact.
Start by marking the pocket size on the scrap fabric. Cut a mock-up with the planned ease, then attach a temporary zipper or fold the opening to mimic one. Test the fit before you cut the jacket. This step can reveal a cramped opening or awkward angle while changes are still easy.
For the finished pocket:
- Keep the pocket bag clear of the armhole, vents, closures, and existing structural seams.
- Attach it to a stable lining area or seam allowance, not unsupported lining alone.
- Reinforce the pocket corners, where pulling can concentrate.
- Capture the zipper tape fully in the seam and secure both ends.
- Keep stitching even and avoid piercing outer fabric unless the design requires it.
ASTM D6193 is a standard practice for stitches and seams. It can serve as a seam-construction reference, but it does not provide a pocket-load rating. No building-code rule governs garment-pocket construction. Follow the garment and zipper makers’ instructions, and judge the finished work through fit and careful testing.
I would not cut through a structural seam, vent, or closure to gain pocket space. If there is no stable place to anchor the pocket without changing those features, the jacket is not a good candidate for this alteration. A tailor can assess whether the lining or seam allowance offers a safe attachment point.
Load-Test the Pocket and Verify Wearability
A load test is a controlled check of the pocket’s stitching, fabric, and zipper before regular use. It does not certify the pocket or guarantee that it will hold in every situation. Test the pocket outside the body first, then repeat movement checks while wearing the jacket.
If the pocket fabric has no documented specification, sew a sample using the planned fabric, seam, and reinforcement. Load the sample with twice the intended filled-flask mass for 60 seconds. This is a workmanship check, not a certified rating. Stop if the sample stretches, tears, or pulls at the stitching.
Next, test the installed pocket gradually. Start with a light load, then work up to the intended filled-flask mass. Inspect the pocket fabric, corners, zipper tape, slider, and stops after each step. Do not jerk or swing the load to “prove” strength; that adds force in ways the simple check does not measure.
Illustrative fit example: Suppose a filled flask measures 140 mm high and 85 mm wide. A starting pocket interior could be about 150–155 mm deep and 95–100 mm wide, using the stated 10–15 mm ease. The zipper’s clear opening should be at least 105 mm. These figures are an example only; measure your own flask.
With the flask inside, zip the pocket and check the jacket while standing, sitting, bending, and reaching. The pocket should not sag, pull, or obstruct a closure. Stop using it if stitching loosens, the zipper stops shift, or the pocket presses an uncomfortable rigid edge against the body. Avoid carrying a rigid or glass flask where a fall could drive it into you.
Common Questions About Jacket Flask Pockets
These quick answers cover sizing, placement, sewing, and safe testing. They do not replace the jacket maker’s care guidance or a tailor’s inspection of a delicate garment. When the lining or seam construction is uncertain, testing a scrap sample or asking a tailor is safer than cutting first.
How much larger should the pocket be than the flask?
Allow 10–15 mm of extra internal width and depth beyond the flask’s measured size, including its cap.
How wide should the zipper opening be?
The clear opening should be at least 20 mm wider than the flask’s widest point.
Should I measure the flask empty or full?
Measure its shape with the cap on, and weigh it filled as you plan to carry it.
Can I sew the pocket to the jacket lining alone?
Do not assume the lining can support the weight. Anchor the pocket to a stable lining area or seam allowance, and test the construction.
Can I cut a seam to make room?
No. Avoid cutting structural seams, vents, or closures. Choose another location or garment if the pocket does not fit safely.
What if I do not know whether the pocket fabric is strong enough?
Make a sample with the same fabric and stitching. Test it at twice the intended filled-flask mass for 60 seconds; this is only a workmanship check.
Does ASTM D6193 rate pocket strength?
No. It is a reference for stitch and seam construction, not a pocket-load rating.
How do I know the pocket is ready to use?
Test the pocket gradually, inspect the stitching and zipper, then repeat movement checks while wearing the jacket. Stop if it sags, pulls, or blocks movement.
Can I carry a glass flask in the pocket?
A rigid or glass flask may cause injury if you fall. Do not carry one where it could be driven into your body.
Can I use the pocket where bags or containers are screened?
Follow the rules for that place. Do not use a hidden pocket to bypass lawful screening or access controls.
A well-planned pocket should hold its shape, open without strain, and stay out of the way as you move. Measure first, mock up the fit, and test the finished work with care. If the jacket’s lining or seams cannot support the pocket without damage, leave the garment intact and ask a tailor about alternatives.
(This article was written by one of our staff writers, Ethan Caldwell. Visit our Meet the Team page.)
