diff --git a/doc/changelog.md b/doc/changelog.md
index 06ed8ba8..a2cfd955 100644
--- a/doc/changelog.md
+++ b/doc/changelog.md
@@ -2,6 +2,10 @@
 
 # Change Log
 
+## Feb-2-2024: Version 2.9.2
+
+- `boundary_mfp` value is stored in `kappa-*.hdf5` file when it is specified.
+
 ## Dec-26-2023: Version 2.9.1
 
 - Release to build conda-forge package.
diff --git a/doc/command-options.md b/doc/command-options.md
index 2e815fa0..a8b969d7 100644
--- a/doc/command-options.md
+++ b/doc/command-options.md
@@ -561,6 +561,8 @@ Then running with isotope calculation:
 In the result hdf5 file, currently isotope scattering strength is not written
 out, i.e., `gamma` is still imaginary part of self energy of ph-ph scattering.
 
+(boundary_mfp_option)=
+
 ### `--boundary-mfp`, `--bmfp` (`BOUNDARY_MFP`)
 
 A most simple phonon boundary scattering treatment is included. $v_g/L$ is just
diff --git a/doc/conf.py b/doc/conf.py
index b8f6048f..cae6e3a1 100644
--- a/doc/conf.py
+++ b/doc/conf.py
@@ -60,7 +60,7 @@ copyright = "2015, Atsushi Togo"
 # The short X.Y version.
 version = "2.9"
 # The full version, including alpha/beta/rc tags.
-release = "2.9.1"
+release = "2.9.2"
 
 # The language for content autogenerated by Sphinx. Refer to documentation
 # for a list of supported languages.
diff --git a/doc/hdf5_howto.md b/doc/hdf5_howto.md
index bf90878d..8569eac9 100644
--- a/doc/hdf5_howto.md
+++ b/doc/hdf5_howto.md
@@ -123,8 +123,9 @@ The array shape is (irreducible q-point, phonon band).
 (kappa_hdf5_file_gamma)=
 ### gamma
 
-Imaginary part of self energy. The physical unit is THz, where THz
-is in the ordinal frequency not the angular frequency.
+Imaginary part of self energy of phonon bubble diagram (phonon-phonon
+scattering). The physical unit is THz, where THz is in the ordinal frequency not
+the angular frequency.
 
 The array shape for all grid-points (irreducible q-points) is
 (temperature, irreducible q-point, phonon band).
@@ -262,9 +263,16 @@ P_{\mathbf{q}j} = \frac{1}{(3n_\mathrm{a})^2} \sum_{\lambda'\lambda''}
 $$
 
 This is not going to be calculated in the RTA thermal coductivity
-calculation mode by default. To calculate this, `--full_pp` option
+calculation mode by default. To calculate this, `--full-pp` option
 has to be specified (see {ref}`full_pp_option`).
 
+### boundary_mfp
+
+A value specified by {ref}`boundary_mfp_option`. The physical unit is
+micrometre.
+
+When `--boundary-mfp` option is explicitly specified, its value is stored here.
+
 ### kappa_unit_conversion
 
 This is used to convert the physical unit of lattice thermal
diff --git a/phono3py/version.py b/phono3py/version.py
index a38d4d39..434dd992 100644
--- a/phono3py/version.py
+++ b/phono3py/version.py
@@ -34,4 +34,4 @@
 # ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
 # POSSIBILITY OF SUCH DAMAGE.
 
-__version__ = "2.9.1"
+__version__ = "2.9.2"