The perfect sleeping pad for bikepacking of course depends on the kind of trip you are going on but it always comes down to the factors of warmth (definded by the R-Value), weight, volume and durability. Another one worth looking at is the amount of noise they make when you move around on them.
I'll solely focus on inflatable air mats here as they have been my favorite choice for years now.
R-Value
The R-Value is the best common form of describing the insulation of a sleeping pads from different brands. They still vary a fair amount but the it is a great indicator of what you need to get for the temperatures you'll be facing during your trip.
A rough guideline of the rating you are looking for is:
Summer 1-3
3 Season 3-5
Winter 5+
Shape
There are different shapes of air. Below you can see slim versions as well as an X-Frame. I personally don't own any wide versions as I don't need the space and they add extra weight.
The X-Frame is an interesting one, misunderstood by many. The idea is not really to safe tons of material on have just basic support on super warm days, the ideas is for the X-Frame to be put inside the sleeping bag. Especially down bags. When squeezing the goose down between your back and the ground when lying down, they loose almost all insulation power. By putting the X-Frame inside the sleeping bag you only push down the feathers that are directly underneath the frame and the rest of the sleeping bag is nicely filling the gaps in the X-Frame, creating some nice insulation and warmth. It"s a good combination of creating warmth and saving weight, especially for ultra racing and super light adventures.
There are also half mats which you put only underneath your torso but I dislike them with a passion unless it is really warm nights. Eventually the cold legs will make sleeping uncomfortable and the lack of sleep quality is not worth saving a little packing space and weight.
Thickness / Level of Cushion
Now that is an important one. If you are a side sleeper, I recommend a thickness of 5-10cm. If packing space isn't an issue, the Sea to Summit Eather Light Insulated is my favorite. It inflates to an incredible 10cm, has an R-Value of 3.2, making this a great spring and summer mat and is still fairly small in the way it packs. See photo below.
For racing and shorter adventures I try to pack smaller and mostly look at the lineup for Klymit. The blue Static V has been my companion for the Africa trip and the Static V Insulated UltraLite Slim (the orange one) for the cooler spring nights right now.
The Klymit mats are extremely lightweight and take up super little space. The orange mate below has an R-Value of 4.4 but they also have a very thin material, meaning you need to be very careful when putting them straight on the ground. You want to make sure you clear the ground underneath the mat and avoid any thorns or sharper rocks. I mostly sleep with a bivy bag around my mat and therefore don't have any trouble with it. (a learning from Africa where I pinched the mat several times)
Durability
Generally you can say that by dropping the weight you are also dropping the puncture resistance of an air mat. In most cases. I have found for myself that by giving a little more attention to where I put down my air mat has helped me avoid pinching the ultralite mats and therefore they have become more or less my constant companion. Some sneaky weekend getaways I still opt for the 10cam "glambing style" mat. Even with a few repairs, the blue mat in the middle has been my companion for 3 years now and it is still going strong.
Noise Level
There are 2 things creating noise in an air mat. The general material and the insulation in the insulated mats. Both Sea to Summit and Klymit are fairly low noise (and I am light sleeper) and therefore have become my go to products. I have also heard good things about Thermarest. It is worth spending the few extra Euro and therefore have a pleasant night when sleeping outdoors or in a shelter.
If you got more detailed questions, feel free to drop me a line on Instagram anytime.
Happy riding everybody.