This comes down to how the blanket is constructed.

Waterproof blankets use an internal barrier that prevents liquid from passing through. During washing, water moves into the outer layers but cannot pass through that barrier.

Because of this, some water remains within the outer layers after the wash cycle.

Running an additional spin cycle helps remove excess water before drying.

High heat damages the internal waterproof barrier.

This barrier is what prevents liquid from passing through under pressure. Once it is weakened, the blanket may begin to leak.

Most waterproof failures are caused by heat, not washing itself.

Failure usually comes down to heat and material quality.

Repeated exposure to high temperatures weakens the internal barrier. Lower-quality materials also break down faster under pressure and repeated use.

Waterproof protection ultimately comes down to one thing:
liquid does not pass through.

Once that no longer happens, the product has failed.

Waterproof performance is not about how the blanket looks or feels after washing.

It is defined by whether liquid passes through under pressure.

Handled correctly, the internal waterproof barrier is designed to maintain performance over time.

Liquids often bead on the surface first, then may move into the top layer over time.

This is normal and does not indicate failure.

Waterproof performance is not determined at the surface.

It is defined by whether liquid passes through to what sits underneath.

Pressure forces liquid through materials that are not fully waterproof.

When weight is applied, absorbed moisture is pushed through weaker layers.

A properly constructed waterproof blanket maintains a barrier underneath, preventing penetration even under pressure.

This level of performance is tested under pressure conditions to ensure the waterproof barrier continues to hold when weight is applied.

No.

Water-resistant materials slow absorption but do not stop liquid from passing through.

Waterproof performance means liquid does not pass through, including under pressure.

This usually comes down to material quality.

Lower-grade products often rely on coatings or plastic-like layers that create stiffness and noise.

Higher-quality construction integrates the waterproof barrier internally, allowing the blanket to remain soft, flexible, and quiet.