How slippery are the Fantasy Flight Sleeves?
Fantasy Flight sleeves are quite thick, durable and good quality. They're quite comparable to Ultra Pro sleeves for Magic: The Gathering.

Straight out of the packet, they are very slippery when you first sleeve your decks. Over time, or with some extended shuffling, they will become much less slippery.

The decks in Arkham aren't that tall, so I haven't found the slipperiness to be a problem in practice. Personally, I quite like sleeving in general as it makes the decks easier to shuffle. But if you really don't like slippery decks, and don't have the patience to break them in, then you might want to skip the sleeving.

A few other points to consider.


Buying sleeves for all your cards is fairly expensive, especially if you have lots of expansions.
Storage in the Arkham boxes is already quite tight. Sleeving the cards makes the decks significantly thicker, so that may be an issue.
Consider how much wear the decks receive in practice. If cards aren't shuffled often or aren't being held in-hand for extended periods of time, then sleeving may not be worthwhile.


If you do decide to get them, you'll need the "Mini American" (colour-coded yellow) for the small decks (items, etc.), and "Standard American" (colour-coded green) for the full size decks (e.g. Mythos cards). FFG's sleeving guide will also tell you how many of each pack you'll need, per Arkham expansion.