Travelling with hedgies, advice pls

Hi! I'm soon taking my two babies to a hedgie hotel while I'm away on holiday. The journey to the hotel takes about a 5 minute bike ride, then a heated train, then about 40 minutes on a bus (probably not heated but sheltered from the outside).

What can I do to make warmth for my hedgies in their carriers? They'll have their hidey-s in them, what other material can I use to insulate the carriers? The two carriers will also be in a bigger Bag (like an ikea rainbow bag, if you know which one that is). Is there any material I can stuff the bag with?

I don't have that heating thing you can rub and then it makes warmth for an hour or so unfortunately I forgot to buy them for this occasion ;;_;;

edit: it will be around 5°C that day