During my researches, i have seen that some of the bows and crossbows prods are covered in fur or leather.
Was this traditionnally done to prevent the metal or wood to be affected by the cold? Was it really effective?

Personally, I think,the crossbows was covered in fur or leather to protect it from freezing during winter. If you have a frozen crossbow, it tends to be more brittle (i.e. easy to be broken).

Do you happen to have a picture of the crossbow (in fur/leather), which you're talking about?

While I don't disagree that cold would make the metal more brittle, I think it is for a much more practical reason.
Have you ever held metal in freezing weather?

If it is a bow as opposed to a crossbow, the explanation may also be that it was part of the binding for a composite bow. Were composite bows used at this time?

I'm no expert but it occurs to me that one of the uses of fur to cover bows and crossbows is to dampen the noise and vibration produced when the arrows are released. Specially in their use for hunting where stealth is of essence. Even today, hunting bows can be found with furry like string silencers

Cheers,

Crossbows were usually made of wood. And wood contains some water. Maybe that's what would make it brittle in winter? Does wood get more brittle if below freezing point?

Yes. It does. Also wood absorbs and releases water with changes in humidity. The properties change dramatically. Bow and bowstrings are weaker when wet. The covering may have been waxed or coated to prevent the bow from getting wet. See the Traditional Bowyer for details.

European crossbow with steel prods had leather covering to protect the shooter from breakage of the bow. (Contain the pieces) My modern copy from Payne-Gallway's drawing requires about 800 or more pounds of force to c**k it. If it were to break the shooter could get injured. I have not made the leather cover yet but this has reminded me to do so. European crossbows had laminated prods probably as early as the 1100. (wood/horn/bone/sinew) Even these weaker bows might be dangerous if they broke.

I would think the Chinese also had laminated prods at the same time. Does anyone know for sure?

Replica 15th European Crossbow with steel prod (~800 pound) requires a windless to c**k.

I recently came across this outstanding site which deals with all sorts of bows and crossbows from China and neighbouring countries:

http://www.atarn.org/letters/letter_summaries.htm