% Transparent schematic views of the standard elementary cap-direction foams.
% The slice coordinate increases upwards. Black: boundary web. Blue: seams.
\begin{tikzpicture}[x={(.85cm,0cm)},y={(.38cm,.40cm)},z={(0cm,.95cm)},
  line cap=round,line join=round,
  sheet/.style={fill=foamFloor,fill opacity=.7,draw=none},
  wall/.style={fill=black!7,fill opacity=.6,draw=none},
  boundary/.style={black,line width=.85pt},
  seam/.style={foamBlue,line width=1.05pt},
  collar/.style={black!40,line width=.45pt}]
\begin{scope}
  \coordinate (l) at (-1,0,0);\coordinate (r) at (1,0,0);
  \coordinate (u) at (0,.65,0);\coordinate (d) at (0,-.65,0);
  \coordinate (q) at (0,0,.85);
  \coordinate (el) at (-1.7,0,0);\coordinate (er) at (1.7,0,0);
  \coordinate (tl) at (-1.7,0,1.9);\coordinate (tr) at (1.7,0,1.9);
  \path[wall] (el)--(l)--(q)--(r)--(er)--(tr)--(tl)--cycle;
  \path[sheet] (l)--(u)--(r)--(q)--cycle;
  \path[sheet] (l)--(d)--(r)--(q)--cycle;
  \draw[collar] (el)--(tl) (er)--(tr);
  \draw[boundary] (el)--(l)--(u)--(r)--(er) (l)--(d)--(r) (tl)--(tr);
  \draw[seam] (l)--(q)--(r);
  \foreach \v in {l,r}{\fill (\v) circle[radius=1.3pt];}
  \draw[-{Latex[length=1.7mm]},black!55] (-2.35,0,.2)--(-2.35,0,1.6)
    node[midway,left,font=\footnotesize] {$t$};
  \node[font=\small] at (0,0,3.05) {Bigon};
  \node[font=\footnotesize,align=center] at (0,0,-1.35)
    {two disks on a common seam\\and one sheet continuing upwards};
\end{scope}
\begin{scope}[shift={(7,0,0)}]
  \coordinate (a) at (-1,-.6,0);\coordinate (b) at (1,-.6,0);
  \coordinate (c) at (0,1,0);
  \coordinate (ea) at (-1.6,-.96,0);\coordinate (eb) at (1.6,-.96,0);
  \coordinate (ec) at (0,1.6,0);
  \coordinate (ta) at (-1.6,-.96,2);\coordinate (tb) at (1.6,-.96,2);
  \coordinate (tc) at (0,1.6,2);
  \coordinate (T) at (0,-.067,1);\coordinate (v) at (0,-.067,2);
  \path[wall] (c)--(ec)--(tc)--(v)--(T)--cycle;
  \path[wall] (a)--(ea)--(ta)--(v)--(T)--cycle;
  \path[wall] (b)--(eb)--(tb)--(v)--(T)--cycle;
  \path[sheet] (a)--(b)--(T)--cycle;
  \path[sheet] (b)--(c)--(T)--cycle;
  \path[sheet] (c)--(a)--(T)--cycle;
  \draw[collar] (ea)--(ta) (eb)--(tb) (ec)--(tc);
  \draw[boundary] (a)--(b)--(c)--cycle (ea)--(a) (eb)--(b) (ec)--(c)
    (ta)--(v)--(tb) (v)--(tc);
  \draw[seam] (a)--(T)--(b) (c)--(T)--(v);
  \foreach \w in {a,b,c,v}{\fill (\w) circle[radius=1.3pt];}
  \fill[foamBlue] (T) circle[radius=2.2pt];
  \node[font=\footnotesize,text=foamBlue,right=3pt] at (T) {$T$};
  \node[font=\small] at (0,0,3.05) {Triangle};
  \node[font=\footnotesize,align=center] at (0,0,-1.35)
    {four seams meet at $T$;\\$T$ is a tetrahedral point};
\end{scope}
\begin{scope}[shift={(0,0,-6)}]
  \coordinate (a) at (-.9,-.9,0);\coordinate (b) at (.9,-.9,0);
  \coordinate (c) at (.9,.9,0);\coordinate (d) at (-.9,.9,0);
  \coordinate (ea) at (-1.45,-1.45,0);\coordinate (eb) at (1.45,-1.45,0);
  \coordinate (ec) at (1.45,1.45,0);\coordinate (ed) at (-1.45,1.45,0);
  \coordinate (ta) at (-1.45,-1.45,1.9);\coordinate (tb) at (1.45,-1.45,1.9);
  \coordinate (tc) at (1.45,1.45,1.9);\coordinate (td) at (-1.45,1.45,1.9);
  \coordinate (p) at (0,-.9,.9);\coordinate (q) at (0,.9,.9);
  \path[wall] (ed)--(d)--(q)--(c)--(ec)--(tc)--(td)--cycle;
  \path[sheet] (a)--(p)--(b)--(c)--(q)--(d)--cycle;
  \path[sheet] (a)--(b)--(p)--cycle;
  \path[sheet] (c)--(d)--(q)--cycle;
  \path[wall] (ea)--(a)--(p)--(b)--(eb)--(tb)--(ta)--cycle;
  \draw[collar] (ea)--(ta) (eb)--(tb) (ec)--(tc) (ed)--(td);
  \draw[boundary] (a)--(b)--(c)--(d)--cycle
    (ea)--(a) (eb)--(b) (ec)--(c) (ed)--(d) (ta)--(tb) (tc)--(td);
  \draw[seam] (a)--(p)--(b) (c)--(q)--(d);
  \foreach \v in {a,b,c,d}{\fill (\v) circle[radius=1.3pt];}
  \node[font=\small] at (0,0,3.05) {Square: one of the two resolutions};
  \node[font=\footnotesize,align=center] at (0,0,-1.35)
    {two seam arcs; rotate the local picture\\through $90^\circ$ for the other resolution};
\end{scope}
\begin{scope}[shift={(7,0,-6)}]
  \coordinate (l) at (-1.5,0,0);\coordinate (r) at (1.5,0,0);
  \coordinate (u) at (0,.9,0);\coordinate (d) at (0,-.9,0);
  \coordinate (q) at (0,0,1.45);
  \path[sheet] (l)--(u)--(r)--(q)--cycle;
  \path[sheet] (l)--(r)--(q)--cycle;
  \path[sheet] (l)--(d)--(r)--(q)--cycle;
  \draw[boundary] (l)--(u)--(r)--(d)--cycle (l)--(r);
  \draw[seam] (l)--(q)--(r);
  \foreach \v in {l,r}{\fill (\v) circle[radius=1.3pt];}
  \node[font=\small] at (0,0,3.05) {Terminal theta cap};
  \node[font=\footnotesize,align=center] at (0,0,-1.35)
    {three disks sharing one seam interval;\\the outgoing web is empty};
\end{scope}
\end{tikzpicture}