"i-Size" is often used as shorthand for newer European child-seat rules, but the precise approval shown on a seat is UN R129. ECE R44/04 is the older weight-based approval. New-sale rules have shifted toward R129 across the EU, while questions about continued use of an existing R44/04 seat require current national guidance. Check official Czech and EU information for your travel date.
How the approvals differ
R44/04 groups seats primarily by child weight. R129 uses stature as a central selection measure, includes updated testing requirements, and sets a minimum rear-facing period for young children. Some R129 seats are i-Size models designed around standardized vehicle seating envelopes, while not every R129 product is marketed or installed in exactly the same way. Read the orange approval label and manual rather than relying on a shop category.
What R129 does not guarantee
An R129 label does not mean universal fit in every car, easy installation, or suitability for every child in the printed height range. Vehicle seats, belt geometry, ISOFIX positions, floor storage compartments, and available cabin space all matter. Check the manufacturer's compatibility list where provided and confirm whether a support leg, top tether, base, or vehicle belt is required.
Using an older approved seat
Do not assume that a ban on new sales automatically makes every existing R44/04 seat illegal to use, or that continued legal use makes an old seat the best choice. Verify current Czech rules. Also consider expiry or service-life guidance, recall status, labels, full instructions, missing parts, and collision history. Never use a secondhand seat with an unknown history.
Questions for a rental provider
- What is the exact model and approval regulation?
- What child stature or weight range applies?
- Does it install rear-facing for this child?
- Is a base, top tether, or support leg supplied?
- Has vehicle compatibility been checked?
At pickup, compare the answer with the seat label and manual. A brand name alone is insufficient.