Picnic blankets are bought from a photograph of a dry lawn and judged on damp grass. These four checks cover the gap.

Ask what the film is, by name

Not “waterproof”, not “water-resistant” — the actual material. A bonded PU or TPU laminate does not pass ground water. A thin PEVA or PVC sheet or a coated woven back does, fairly quickly.

Any supplier who has specified their own product can tell you which it is. One who cannot is telling you something useful anyway.

Ask how it is attached

This matters more than the film. Laminated to the face, the two layers behave as one fabric. Sewn on only at the perimeter, they separate in use, water gets between them and the blanket bags out.

Pinch the centre of a sample. If the layers slide independently, it is not a laminate.

Plan for the fold, or avoid it

A blanket is creased in the same places every time it is put away. Cheap films crack along those lines, and then it leaks straight across the middle.

Specify a backing chosen for flex, and buy the version with a strap, because the strap is what makes people roll it instead of folding it.

Match the face to the ground

Cut grass and dry sand fall off a tight, low-pile, smooth face with one shake, and bed permanently into a brushed or looped one.

It is decided at the yarn and finish stage, before anything is bonded, and it costs nothing to get right. It is also the single most common thing customers complain about after the first outing.

Read the care instruction before you buy, not after

Hot washing and tumble drying delaminate a laminate. A bonded blanket is wiped or cold-washed and dried flat.

If there is no sewn-in care label, the first wash is a coin toss. Ask for one; it costs almost nothing and it prevents most returns in this category.