Cover warping

„How to avoid cover warping“

Hardcover warping – is a clearly noticeable hardcover book deformation when the cover bends outwards on the open side of the book. This phenomenon appears due to different levels of humidity between interior block, cover board and covering material, also due to specific microclimate conditions in the manufacturer and storage facilities.  Heating season usually has the most significant impact on hardcover warping effect, due to very low air humidity inside heated facilities. Book drying process (starting from the open side of the book, continuing towards the spine) creates a tension which causes covers to warp. 

Due to inevitability of such process cover warping that does not exceed 5 mm is not considered a production defect.

Factors contributing to hardcover warping:

Factor impact level on scale 


(1-5)    Factors

5 Winter / heating season

5 Pages with partial ink / varnish coverage, when unprinted margins are 3-4 cm wide

5 Interior book block is thinner than 3 mm.

4 Coated art interior paper.

3 Coated interior paper.

3 High humidity of the cover (above 50%).

3 Coated or wrong grain direction paper for endpapers.

3 High humidity of the interior book block (from 45 to 55%).

3 Interior book block thinner than 5 mm.

3 Landscape orientation.

3 Cover board thinner than 2 mm.

3 Pages with full area ink / varnish coverage (dispersion varnish = humidity barrier).

2 Interior book block thinner than 8 mm.

2 Light coated interior paper.

1 Transportation with regular (not thermo-regulated) truck during winter season.

1 Interior book block thinner than 10 mm.

1 Covering and endpaper materials are not balanced.

Hardcover warping effect will be more significant, when two or more of these factors will be involved in the production and the sum of factor impact score will be more than 10. This informational sheet is based on experience of book manufacturing experts and should be evaluated and supplemented with consideration to each individual case of hardcover production.

Precautionary measures to help avoid the hardcover warping problem:

  • While planning hardcover production try to avoid the accumulation of above mentioned factors;
  • Use uncoated paper for end-papers rather than coated;
  • Plan-in an additional day for binding process, so the books can get acclimatized. Materials will have a better chance of drying before entering different environment.
  • Advise your clients to store the books in facilities that can ensure suitable microclimate – relative air humidity 45-55%. Also, such conditions are optimal for humans.
  • Discuss each individual production with your bindery in advance to estimate how probable the appearance of hardcover warping effect is.