Winter coats and car seats: why the harness has to go under

This is the winter question we get asked most, and the physics behind the answer is simple enough to explain in a paragraph. A thick coat takes up space. In a crash that space disappears instantly, and the harness that was snug over the coat is suddenly loose over the child.

What compression means in practice

A puffy jacket can be several centimetres thick and compresses to almost nothing under load. That slack has to go somewhere, and where it goes is forward movement of the child inside the harness — exactly what the harness exists to prevent.

The effect is not subtle. This is why every car seat manual and every safety authority says the same thing about bulky outerwear.

The pinch test tells you

Buckle the child in with the coat on and tighten the harness normally. Then, without loosening anything, take the child out, remove the coat, and put them back in the harness at the same setting. If you can now pinch a horizontal fold of webbing at the shoulder, the coat was creating slack.

It is a two-minute demonstration and it is far more convincing than being told.

What to do instead

Dress the child in thin, warm layers — fleece rather than down — buckle the harness properly, and then put the coat on backwards over the top like a blanket, arms through the sleeves. A blanket over the buckled harness works just as well.

Both approaches keep the child warm and keep the harness against the body, which is the only arrangement that works.

Warm the car, not the child

The most practical answer in a cold winter is to run the car for a few minutes before loading, so the child is only outdoors briefly. A car that is warm inside removes the whole problem.

Remote start, where a car has it, is genuinely useful for this and for nothing else in particular.

Aftermarket covers and inserts

Products that go between the child and the harness, or that add padding behind the back, are not part of the tested system and are not permitted unless they were supplied with the seat. That includes many attractive-looking “car seat ponchos” and fleece inserts sold separately.

Covers that go over the outside of the seat, without touching the harness path, are generally acceptable — but check the manual, because manufacturers differ.

Bulky footwear and hats

Boots and hats are less critical because they are not under the harness, but a hard-brimmed hat can push the head forward against the shell. A soft hat is fine.

Snow boots make it harder to check whether the buckle is doing up properly, so glance down rather than going by feel.

Older children and boosters

The same principle applies to a booster: the lap belt has to sit low across the hips, and a thick coat lifts it onto the abdomen. Coat off, belt on, coat over the top is the same routine.

Children who buckle themselves need this explained once rather than enforced daily; they generally get it immediately once shown the pinch test.

A winter routine that works

Warm the car, thin layers on, harness tight with the pinch test passed, coat over the top. Keep a spare blanket in the boot for the days you forget. If you want to see the pinch test demonstrated on the seat you actually own, bring it to the counter on Northern Boulevard.

What to keep in the car through the winter

A blanket in the boot solves this problem permanently, and it is worth putting one in each car in November rather than remembering it in January. A spare fleece layer in the same bag covers the days when the thin layer you dressed the child in turns out not to be enough at the other end of the journey.

Keep both somewhere reachable from the driver’s seat. Anything in the boot behind a pushchair is effectively not in the car when it is raining and you are parked on a busy street.

Snowsuits and older children

The same physics applies to a snowsuit, and snowsuits are bulkier than coats. For a child who needs one on arrival, the practical routine is to travel in a fleece and put the snowsuit on at the destination, or to use a suit that unzips fully so it can be worn open over the harness.

For a booster-age child, the lap belt is the thing to watch: a bulky suit lifts it off the hips onto the soft abdomen, which is exactly what a booster exists to prevent. Coat off, belt on, coat over the top works at every age.

The short version

• Bulky coats compress; the harness that felt snug becomes loose.
• Do the pinch test with the coat off, then again with whatever the child wears.
• Put the coat on backwards over the buckled harness, or use a blanket.
• Warm the car rather than dressing for the outdoors inside it.

From our shelves

• Graco TurboBooster 2.0 Highback Booster Car Seat, Declan — $69.99
• Graco Tranzitions 3-in-1 Harness Booster Car Seat, Forward Facing Car Seat, Highback — $139.99
• Graco Tranzitions 3-in-1 Harness Booster Car Seat, Forward Facing Car Seat, Highback — $139.99

Where to go next

Browse the full range on the shop page, read the frequently asked questions before ordering, or check delivery timing on the Shipping Policy page. If you would rather ask a person, contact us — the phone reaches the counter.